It is a good try to submit after 5.28 and to ask ur employer to make u a valid job letter.Yes, I'm not working from April 13th to May 12th. Also my employer didn't promised that business will start again in may 12th. So it's unpredictable.
Do goverment is giving any kind of relief in hours because of this pandemic?
Two risks may appear:
1. I’ve seen ppl who did that month-and-day thing but failed, because some officers considered the time u’ve invited should be qualified ahead and the work exp is locked once ITA is given. (Right, it’s their problem of not updating the system by adding the stupid date option, but nothing we can do to change their judgement if it’s been made).
2.Even if passing 5.28 to submit the application is fine, there may be another problem as the officer want u to provide payroll, tax or other document to support the job letter. Since u stopped working now, I don’t know if ur employer is able to help u this much or not.
If u won’t face losing points issue in a year (like because of age, etc) and r ready for the torture of waiting for the final decision, u could accept this one and wait for the officer’s decision.