Vacuum leak test in filled vials

In Desiccator type leak test apparatus what is required vacuum and hold time of leak test for dry powder filled vials.any reference?

Please go through,USP31<381>.
ISO 8362 annexure C (modified ISO)

In usp time at vacuum is 10minute.and time at ambient is 30 minute.
What is time at ambient?

Time at vacuum hold is 30 min with -37KPa.and time at ambient is 30 minutes are we are ISO.
Even though USP is given 10 minutes hold with vacuum -27kpa.and 30minutes hold at ambient,we are going to higher one.

Can we reduce the hold time by increasing the vacuum level?suppose -54kpa for 3 minute.