When casting spells with a duration longer than instantaneous, at what point in the round does the effect expire? Say for example you cast a spell with a duration of 1 round, does that mean the spell ends at the end of your turn or at the beginning of your next turn? I've checked the SRD and can't find anything solid that clearly explains when the effects of spells run out.
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: