diff --git a/python/ray/tune/trial.py b/python/ray/tune/trial.py
index 3ef0b5027a46..7f32d3941ed8 100644
--- a/python/ray/tune/trial.py
+++ b/python/ray/tune/trial.py
@@ -26,7 +26,7 @@
 import ray.tune.registry
 from ray.tune.result import (DEFAULT_RESULTS_DIR, DONE, HOSTNAME, PID,
                              TIME_TOTAL_S, TRAINING_ITERATION, TIMESTEPS_TOTAL)
-from ray.utils import random_string, binary_to_hex, hex_to_binary
+from ray.utils import _random_string, binary_to_hex, hex_to_binary
 
 DEBUG_PRINT_INTERVAL = 5
 MAX_LEN_IDENTIFIER = 130
@@ -311,7 +311,7 @@ def _registration_check(cls, trainable_name):
 
     @classmethod
     def generate_id(cls):
-        return binary_to_hex(random_string())[:8]
+        return binary_to_hex(_random_string())[:8]
 
     def init_logger(self):
         """Init logger."""
diff --git a/python/ray/worker.py b/python/ray/worker.py
index fb3ad9025c38..f66616b3800c 100644
--- a/python/ray/worker.py
+++ b/python/ray/worker.py
@@ -38,7 +38,7 @@
 from ray import profiling
 from ray.function_manager import (FunctionActorManager, FunctionDescriptor)
 import ray.parameter
-from ray.utils import (check_oversized_pickle, is_cython, random_string,
+from ray.utils import (check_oversized_pickle, is_cython, _random_string,
                        thread_safe_client, setup_logger)
 
 SCRIPT_MODE = 0
@@ -186,7 +186,7 @@ def task_context(self):
                 # to the current task ID may not be correct. Generate a
                 # random task ID so that the backend can differentiate
                 # between different threads.
-                self._task_context.current_task_id = TaskID(random_string())
+                self._task_context.current_task_id = TaskID(_random_string())
                 if getattr(self, '_multithreading_warned', False) is not True:
                     logger.warning(
                         "Calling ray.get or ray.wait in a separate thread "
@@ -1753,13 +1753,13 @@ def connect(info,
 
     # Initialize some fields.
     if mode is WORKER_MODE:
-        worker.worker_id = random_string()
+        worker.worker_id = _random_string()
         if setproctitle:
             setproctitle.setproctitle("ray_worker")
     else:
         # This is the code path of driver mode.
         if driver_id is None:
-            driver_id = DriverID(random_string())
+            driver_id = DriverID(_random_string())
 
         if not isinstance(driver_id, DriverID):
             raise Exception("The type of given driver id must be DriverID.")
@@ -1911,7 +1911,7 @@ def connect(info,
             function_descriptor.get_function_descriptor_list(),
             [],  # arguments.
             0,  # num_returns.
-            TaskID(random_string()),  # parent_task_id.
+            TaskID(_random_string()),  # parent_task_id.
             0,  # parent_counter.
             ActorID.nil(),  # actor_creation_id.
             ObjectID.nil(),  # actor_creation_dummy_object_id.
@@ -2164,7 +2164,7 @@ def register_custom_serializer(cls,
         else:
             # In this case, the class ID only needs to be meaningful on this
             # worker and not across workers.
-            class_id = random_string()
+            class_id = _random_string()
 
         # Make sure class_id is a string.
         class_id = ray.utils.binary_to_hex(class_id)
diff --git a/src/ray/object_manager/test/object_manager_test.cc b/src/ray/object_manager/test/object_manager_test.cc
index 904f1ed2a83c..a6d79d608e97 100644
--- a/src/ray/object_manager/test/object_manager_test.cc
+++ b/src/ray/object_manager/test/object_manager_test.cc
@@ -342,27 +342,27 @@ class TestObjectManager : public TestObjectManagerBase {
     case 0: {
       // Ensure timeout_ms = 0 is handled correctly.
       // Out of 5 objects, we expect 3 ready objects and 2 remaining objects.
-      TestWait(100, 5, 3, /*timeout_ms=*/0, false, false);
+      TestWait(600, 5, 3, /*timeout_ms=*/0, false, false);
     } break;
     case 1: {
       // Ensure timeout_ms = 1000 is handled correctly.
       // Out of 5 objects, we expect 3 ready objects and 2 remaining objects.
-      TestWait(100, 5, 3, /*timeout_ms=*/1000, false, false);
+      TestWait(600, 5, 3, /*timeout_ms=*/1000, false, false);
     } break;
     case 2: {
       // Generate objects locally to ensure local object code-path works properly.
       // Out of 5 objects, we expect 3 ready objects and 2 remaining objects.
-      TestWait(100, 5, 3, 1000, false, /*test_local=*/true);
+      TestWait(600, 5, 3, 1000, false, /*test_local=*/true);
     } break;
     case 3: {
       // Wait on an object that's never registered with GCS to ensure timeout works
       // properly.
-      TestWait(100, /*num_objects=*/5, /*required_objects=*/6, 1000,
+      TestWait(600, /*num_objects=*/5, /*required_objects=*/6, 1000,
                /*include_nonexistent=*/true, false);
     } break;
     case 4: {
       // Ensure infinite time code-path works properly.
-      TestWait(100, 5, 5, /*timeout_ms=*/-1, false, false);
+      TestWait(600, 5, 5, /*timeout_ms=*/-1, false, false);
     } break;
     }
   }
diff --git a/test/actor_test.py b/test/actor_test.py
index 8a4d2ea3f992..230a5db30546 100644
--- a/test/actor_test.py
+++ b/test/actor_test.py
@@ -1074,7 +1074,7 @@ def check_intervals_non_overlapping(list_of_intervals):
     @ray.remote(num_gpus=1)
     def f1():
         t1 = time.monotonic()
-        time.sleep(0.2)
+        time.sleep(0.4)
         t2 = time.monotonic()
         gpu_ids = ray.get_gpu_ids()
         assert len(gpu_ids) == 1
@@ -1085,7 +1085,7 @@ def f1():
     @ray.remote(num_gpus=2)
     def f2():
         t1 = time.monotonic()
-        time.sleep(0.2)
+        time.sleep(0.4)
         t2 = time.monotonic()
         gpu_ids = ray.get_gpu_ids()
         assert len(gpu_ids) == 2
@@ -1186,7 +1186,7 @@ def test_actors_and_tasks_with_gpus_version_two(shutdown_only):
 
     @ray.remote(num_gpus=1)
     def f():
-        time.sleep(4)
+        time.sleep(5)
         gpu_ids = ray.get_gpu_ids()
         assert len(gpu_ids) == 1
         return gpu_ids[0]