What are the chances of an abstract being accepted if it is a day late for a conference Will an abstract sent a day late or few hours late be considered for a competitive conference?
It depends on the conference. Some conferences use online systems that stop allowing submissions after the deadline. For these conferences you might be able to eventually get in touch with a program chair or administrator and get your abstract considered, but you may also run into everyone telling you that you missed the deadline. Other conferences you email the abstract to the program chair or administrator. Again, you may be told you missed the deadline or they may allow it to be considered.

It is worth noting that many conferences move the deadline, so maybe you are not actually late. Only way to know what is up is to either wait until you hear something or find someone to email/call.