Update microbatch `end_time` to the `batch_size` ceiling

[QMalcolm]

Resolves #10868

Problem

Solution

Checklist

• [ ] I have read the contributing guide and understand what's expected of me.
• [ ] I have run this code in development, and it appears to resolve the stated issue.
• [ ] This PR includes tests, or tests are not required or relevant for this PR.
• [ ] This PR has no interface changes (e.g., macros, CLI, logs, JSON artifacts, config files, adapter interface, etc.) or this PR has already received feedback and approval from Product or DX.
• [ ] This PR includes type annotations for new and modified functions.