they should disable capture availability over night then.
i felt the best thing they could do is every 3 days, have a 12 hour window of availability to steal sigils. If after 12 hours you cant capture the sigils, then they are on cool down for another 3 days. Inside the 12 hours, make it 2-3 hours for sigil corruption, allowing there to be lots of peak battles in clutch situations. Have the 12 hour window be noon to midnight, server location time zone.
Anything else, especially with reduced sigil corruption rates, then kids will just stay at home during the work day, or play at 2 am and capture sigils when nobody is on. And since owning towns are a major thing in factions, that's really bad.