AACOMAS Traffic Guidelines
For DO schools, it looks like the latest is by May 1st.
Per AMCAS, they have deadlines on April 15 to have only 3 schools and April 30 to have only 1 school.
Application and Acceptance Protocols for Applicants
Each TMDSAS school has their own deadlines on when to accept the seat matched. I'm guessing most are before February ends. Schools are also doing rolling waitlist acceptances till May 15. (Edit: TMDSAS also abides by having only 1 school's seat on April 30. Better to assume April 30 for DOs/MDs overall.)
UIWSOM as far as I know did not explicitly give us deadlines after depositing (since the deposit was for a seat). But I'm sure many will start withdrawing as soon as people are sure of which school they want to attend, pending financial aid and other factors confirming a guaranteed seat. Stuff like sending transcripts out and submitting deposits for matched schools are ongoing right now. Some schools don't have deposits, so people may wait till it's safe to withdraw like after receiving a school email/login.