A “round” is a unit of time, effectively equal to the amount of time it takes for the initiative count to return where it was when you started timing. As such, effects with a duration of x rounds end when the initiative count is the same as it was x rounds previous.
Your turn happens “on” an intiative count; the entire turn happens during it. Nonetheless, since effects end as soon as the initiative count ticks to the required count, that is effectively the same as “just before your turn,” assuming your initiative hasn’t changed.
See The Combat Round:
For almost all purposes, there is no relevance to the end of a round or the beginning of a round. A round can be a segment of game time starting with the first character to act and ending with the last, but it usually means a span of time from one round to the same initiative count in the next round. Effects that last a certain number of rounds end just before the same initiative count that they began on.