Is it safe to assume the following?
IHistory.getBarStart(FIVE_MINS,tick.getTime()) == (tick.getTime()%(1000*60*5))

(I would like to use this assumption to avoid a certain dependency on IHistory if possible. However, I don't know whether issues such as leap seconds may cause the assumption to be violated.)

Isak

Yes, because bars consist of ticks (i.e. all bar values like prices and volume are aggregated from ticks within the time frame of the bar).

CORRECTION:
IHistory.getBarStart(FIVE_MINS,tick.getTime()) == tick.getTime()-(tick.getTime()%(1000*60*5))

Thanks. The question was meant to focus on the modular arithmetic: whether leap seconds perturb the alignment of the bar boundaries.

It is more of a "Java time" question than a JForex question, but for the benefit of anyone who may have the same question, here is what I learned:

"in practice, Java represents time/date values as something that’s rather like a mutant version of TAI with seconds that are occasionally 2 seconds long to make it sync back up with UTC–although it claims to be reporting UTC. "

This means that round numbers remain aligned to the bar boundaries, and that it is safe to use simple modular arithmetic to compute bar boundaries.