Good to know it's already in UTC time.

I read the manual on timestamps again and it's a bit confusing. So I asked support this question and they gave this answer:

Question:
When creating an M1 t6 file, what is the timestamp of an M1 bar that covers the period from 11:16:00 - 11:16:59. Is it 11:16:00 or 11:16:59 or 11:17:00 ?

Answer:
it should be 11:16:59.

Unless History.c is displaying it wrong, it looks like your timestamp for this example is 11:17:00.