I am in the same boat. Work plus marathon training has forced me to push back most of my apps to R2.
To answer your questions, yes I think you should let them know and there is nothing to think twice about. If they manage to get them done sooner because you initially gave an earlier deadline then better for you. If they now have more time to complete them and can prioritize accordingly, they'll be happy that you were considerate enough to let them know.
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