guess it depends on several factors, might also vary by region (I'm in DACH) so YMMV.
If it's urgent I'd make a call by phone - I use this rarely if at all (and never did so afterhours), can't remember that I had to wait for more than a minute or so in the last years. With email it varies - usually I get a response (call or email) in the next two hours (if your mail is not picked up within a certain time you get an automated response indicating this). I assume that the content of your request is taken into account - thus if you afterhours report a problem saying you are now struggling with this or that for three weeks you'll likely not get a response before the next business day.
That's general support - questions in relation to sample submissions seem to get worked on the same regardless of the time (even if they are of general nature).
That's of course only my personal experience and not statistically significant :smileywink:
Is this just a hypothetical question or did (do) you have a particular issue?
