not a concern in vege phase at all... even middle of the dark cycle.
The issue is flower phase -- uninterrupted darkness is essential. 12/12 affords some leeway. 13/11 will work for most marijuana plants, too, so a little light a few minutes after is no big deal, but interrupting later on is a big deal.
No, 3-4 minutes after the lights go out, even in flower, is not a concern. An hour or more becomes a concern. Interrupting deeper into the dark cycle is a major concern, too.
Just in case -- bro science used to say 'green light is safe' -- it is not. In fact, research shows green light causes a reaction more quickly than the other wavelengths. It's actually worse. This is just one example of why you should alays have a healthy skepticism of anecdotes. Sometimes what is popular is correct, but often times it is not.
There should never be a reason to interrupt the dark cycle. If it is the case, plan better in future. Definitely don't cause light pollution during flower phase.