diff --git a/src/lib/duration-flags.test.ts b/src/lib/duration-flags.test.ts
new file mode 100644
index 00000000000..ff05916e0bd
--- /dev/null
+++ b/src/lib/duration-flags.test.ts
@@ -0,0 +1,27 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+import { describe, expect, it } from "vitest";
+
+import { parseLogsSinceDuration, parseShieldsTimeoutDuration } from "./duration-flags";
+
+describe("oclif duration flag parsers", () => {
+  it("normalizes logs --since durations", () => {
+    expect(parseLogsSinceDuration(" 5m ")).toBe("5m");
+    expect(parseLogsSinceDuration("30s")).toBe("30s");
+  });
+
+  it("rejects invalid logs --since durations with the public parser message", () => {
+    expect(() => parseLogsSinceDuration("0s")).toThrow(
+      "--since requires a positive duration like 5m, 1h, or 30s",
+    );
+    expect(() => parseLogsSinceDuration("someday")).toThrow(
+      "--since requires a positive duration like 5m, 1h, or 30s",
+    );
+  });
+
+  it("uses the shields duration parser for bounded shields timeouts", () => {
+    expect(parseShieldsTimeoutDuration(" 5m ")).toBe("5m");
+    expect(() => parseShieldsTimeoutDuration("2h")).toThrow(/exceeds maximum/);
+  });
+});
diff --git a/src/lib/duration-flags.ts b/src/lib/duration-flags.ts
new file mode 100644
index 00000000000..d5a391313e4
--- /dev/null
+++ b/src/lib/duration-flags.ts
@@ -0,0 +1,35 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+import { Errors, Flags } from "@oclif/core";
+
+import { parseDuration } from "./duration";
+
+const LOGS_SINCE_DURATION_RE = /^[1-9]\d*(?:ms|s|m|h|d)$/i;
+
+export function parseLogsSinceDuration(input: string): string {
+  const trimmed = input.trim();
+  if (!LOGS_SINCE_DURATION_RE.test(trimmed)) {
+    throw new Errors.CLIError("--since requires a positive duration like 5m, 1h, or 30s");
+  }
+  return trimmed;
+}
+
+export function parseShieldsTimeoutDuration(input: string): string {
+  const trimmed = input.trim();
+  try {
+    parseDuration(trimmed);
+  } catch (error) {
+    const message = error instanceof Error ? error.message : String(error);
+    throw new Errors.CLIError(message);
+  }
+  return trimmed;
+}
+
+export const logsSinceDurationFlag = Flags.custom<string>({
+  parse: async (input) => parseLogsSinceDuration(input),
+});
+
+export const shieldsTimeoutDurationFlag = Flags.custom<string>({
+  parse: async (input) => parseShieldsTimeoutDuration(input),
+});
diff --git a/src/lib/sandbox-logs-cli-command.ts b/src/lib/sandbox-logs-cli-command.ts
index 47e399d3b90..e20312dbf71 100644
--- a/src/lib/sandbox-logs-cli-command.ts
+++ b/src/lib/sandbox-logs-cli-command.ts
@@ -5,6 +5,7 @@
 
 import { Args, Command, Flags } from "@oclif/core";
 
+import { logsSinceDurationFlag } from "./duration-flags";
 import type { SandboxLogsOptions } from "./sandbox-logs-options";
 import { DEFAULT_SANDBOX_LOG_LINES } from "./sandbox-logs-options";
 import { showSandboxLogs } from "./sandbox-runtime-actions";
@@ -13,7 +14,6 @@ type SandboxLogsRuntimeBridge = {
   sandboxLogs: (sandboxName: string, options: SandboxLogsOptions) => void;
 };
 
-const LOGS_SINCE_DURATION_RE = /^[1-9]\d*(?:ms|s|m|h|d)$/i;
 const DEFAULT_SANDBOX_LOG_LINE_COUNT = Number(DEFAULT_SANDBOX_LOG_LINES);
 
 let runtimeBridgeFactory = (): SandboxLogsRuntimeBridge => ({ sandboxLogs: showSandboxLogs });
@@ -56,28 +56,17 @@ export default class SandboxLogsCommand extends Command {
       description: "Number of log lines to return",
       min: 1,
     }),
-    since: Flags.string({
+    since: logsSinceDurationFlag({
       description: "Only show logs from this duration ago, such as 5m, 1h, or 30s",
     }),
   };
 
-  private normalizeSinceDuration(since: string | undefined): string | null {
-    if (since === undefined) {
-      return null;
-    }
-    const trimmed = since.trim();
-    if (!LOGS_SINCE_DURATION_RE.test(trimmed)) {
-      this.error("--since requires a positive duration like 5m, 1h, or 30s", { exit: 2 });
-    }
-    return trimmed;
-  }
-
   public async run(): Promise<void> {
     const { args, flags } = await this.parse(SandboxLogsCommand);
     getRuntimeBridge().sandboxLogs(args.sandboxName, {
       follow: flags.follow === true,
       lines: String(flags.tail),
-      since: this.normalizeSinceDuration(flags.since),
+      since: flags.since ?? null,
     });
   }
 }
diff --git a/src/lib/shields-cli-commands.ts b/src/lib/shields-cli-commands.ts
index 7811f69f66a..608b0fbbb31 100644
--- a/src/lib/shields-cli-commands.ts
+++ b/src/lib/shields-cli-commands.ts
@@ -5,6 +5,7 @@
 
 import { Args, Command, Flags } from "@oclif/core";
 
+import { shieldsTimeoutDurationFlag } from "./duration-flags";
 import * as shields from "./shields";
 
 const sandboxNameArg = Args.string({
@@ -23,7 +24,7 @@ export class ShieldsDownCommand extends Command {
   static args = { sandboxName: sandboxNameArg };
   static flags = {
     help: Flags.help({ char: "h" }),
-    timeout: Flags.string({ description: "Duration before shields are restored" }),
+    timeout: shieldsTimeoutDurationFlag({ description: "Duration before shields are restored" }),
     reason: Flags.string({ description: "Reason for lowering shields" }),
     policy: Flags.string({ description: "Policy to apply while shields are down" }),
   };