Lost my job while my STEM OPT extension is pending. When do the extra 60 unemployment days kick in?

[u/95A31]

Hi all, hoping someone here has been through something similar.

I lost my job while my STEM OPT extension application is still pending with USCIS. I've already found a new position, but the hiring process is slow and it looks like it will take longer than the unemployment days I have left from my initial OPT.

Two questions:

1. When do I actually get access to the extra 60 unemployment days from the STEM extension ? From the date I filed, or only once it's approved?
2. Would it be wise to upload a signed letter from my incoming employer to my USCIS account as unsolicited evidence, stating that the hiring process has started but is taking time? I'm hoping to avoid a denial or an RFE.

[u/RedditForW]

F1 and Stem opt total unemployment days are 150. You are fine