It takes an hour to repair a suit of Armor so I think I’d base it off that - I’d probably say 10-30 minutes to resize/reconfigure and “do it properly” but allow a temporary on-the-run resizing in 5-10 that would only last a combat or two (or enable a spacewalk).
In a tense situation, I’d deduct time based on the engineering check as players like it when being really good at a skill grants a visible benefit.
I took a look through the rules and didn't see an exact length of time. I would use the timing for repairing armor as a maximum length of time.
Also, the armorsmithing engineering kit gives a bonus to checks to resize armor. Is it specifically stated that resizing armor requires a check and how to calculate the DC?
If you get secondhand armor that wasn’t tailored for you, you can have it adjusted, which requires a successful Engineering check (DC = 10 + 2 × the armor’s level). Alternatively, you can spend 10% of the armor’s purchase price to have it adjusted by a professional—typically an armorsmith or anyone with multiple ranks in Engineering.
It doesn't list a time, unfortunately, so that's up to your GM.