It's actually every single night, last I checked. Monday nights run a little longer, due to payroll processing. I don't remember the exact hours, but it's pretty much an overnight thing.
Yeah, there's definitely it's fair share of unscheduled maintenance, too. And the scheduled maintenance is always listed as Central time, so if you live out west, it's going to go down for the night much earlier than for everyone else.
After midnight, at the store level, ehr goes into maintenace. Try targetpayandbenefits.com for back door access. Also, ck your password on ehr ta the store, that could be the issue. Login at the store, then at home.