Is the deadline of submitting LoRs the same as that of the application?

[Taxxi]

For example, if the application is due December 15th, do all the LoRs typically have to be submitted (online) by the professors within the same time frame? I am asking this question since I wish I had slightly more time.

[PsyDuck90]

Yes, but programs are usually a bit lenient if the LOR is sent within a day or two. 

[DRMF]

Typically yes, but like PsyDGrad90 said it's usually not too strict. A few schools I applied to had a separate deadline for LORs (e.g. 7 days after the applicant's deadline), but they were in the minority.

If you submit everything on your end, and the LORs don't come in within the time frame you expect them to, you can email program coordinators/administrators (in addition to reminder emails to letter writers) to explain the situation and ask about how soon they're actually going to review the applications; if someone is really nice they will straight tell you "we're meeting next Tue so make sure letters are in by Mon 5 PM", but most probably won't tell you that. If you do have a LOR being submitted more than a couple days late, I would also email the program coordinator to make sure that letter is received and being reviewed as part of your profile.

Overall, if you're just looking to have a few more days to polish your personal statement, I don't think it's worth it to submit everything on your end on the day it's due; I'd rather leave some buffer time for any potential situations happening on the letter writers' end (technical glitch with the website, letter writer sick / on a plane, etc.).