Does it matter?

In my opinion, it doesn't matter, the flower has day and night as you set it, it doesn't know it, but it's just my opinion.

It really wont matter long as its 12/12 for photoperiod strains. If you get a break for when you're running lights from your energy company maybe factor that in to when you start running the setup. I like my flowers to have a similar work schedule as me, up at 6:30am7:00am- off and back from work 6:30pm -7:00pm. Try to have enough time to water and do maintenance so you're not opening that tent and getting light into the room etc.

Shouldn't be a big deal either way. A drastic shift should be avoided, but even those probably don't impact much if at all noticeable. Make sure the dark period remains consistent and long enough ==> all is well. circadian rhythms would be the only concern about a drastic shift, but if necessary for some logistical reason, i'd still do it but not on a whim.