I parked at one of those signs recently, and indeed it took me a bit to figure it out. It should read something like:
Metered parking
2 hour limit
7:00 am-6:30 pm
Mon thru Sat
Metered parking
No limit
6:30 pm-10:00
Mon thru Sat
Free parking
No limit
All other times
My question, of course, is if you park at 4:31 pm, are you good until 10:00 pm, or will you have exceeded the 2-hour limit as of 6:31 pm, even though at that time there is no longer a limit in place? In other words, does the limit apply to the start of your parking time or the end of it? Of course the meter wouldn't sell you enough hours at 4:31 to get you to 10:00 pm, so you'd have to feed the meter at 6:31.