Would 25 days after sex be too late for implantation bleeding?

Timing in cycle: If one has regular cycles, menstrual bleeding occurs at time of expected menses, and is of normal flow. "implantation bleeiding", if it does occur, will happen ~ a week prior to expected menses, and is usually very light, often only spotting. Most women who conceive do not experience noticeable implantation bleeding. If there are any doubts, do home pregnancy test at time of expected menses.

Pregnancy test : If conception was 25 days ago then a pregnancy test would be positive by now. The easiest thing to do is simply take a test and in minutes you will have your answer.