Amend milestone #3 delivery timeline

[juntao]

As discussed here:

#862 (comment)

the milestone #3 task is much greater than we originally envisioned. We need to reconcile changes to the substrate code base since we started and then merge our changes back into the main tree in order to propose an upstream PR and run the most up-to-date performance tests. So, I extended the time needed for this task to 6 months. Thank you.

Project Abstract

Please replace these instructions with a brief description of your project summarising key points (1-2 paragraphs).

If your application is a follow-up to a previous grant, please mention which one in the first line of the abstract and include a link to previous pull requests if applicable.

Grant level

• Level 1: Up to $10,000, 2 approvals
• Level 2: Up to $30,000, 3 approvals
• Level 3: Unlimited, 5 approvals (for >$100k: Web3 Foundation Council approval)

Application Checklist

• The application template has been copied and aptly renamed (project_name.md).
• I have read the application guidelines.
• A BTC, Ethereum (USDC/DAI) or Polkadot/Kusama (aUSD/USDT) address for the payment of the milestones is provided in the application.
• The software delivered for this grant will be released under an open-source license specified in the application.
• The initial PR contains only one commit (squash and force-push if needed).
• The grant will only be announced once the first milestone has been accepted (see the announcement guidelines).
• I prefer the discussion of this application to take place in a private Element/Matrix channel. My username is: @_______:matrix.org (change the homeserver if you use a different one)

[CLAassistant]

All committers have signed the CLA.

[semuelle]

Thanks for the update, @juntao.