1. You mean everybody disappears from the real-time report? that's because the real-time report is thought of for "daily" call-centers, so it looks as back as the last midnight. You can easily change that to support a 24/7 call center by using a "sliding window" of 1.5 times the length of your maximum agent session, eg if your agents stay logged on for 6 hours, you should use 9 to 12 hours to be sure.
#The hour of the day to start realtime monitoring or sXX: sliding window of XX hours
realtime.startHour=s12
this will use a 12-hour sliding window to compute real-time reports.
2. no it does not. It might just be that at 6 or 7 pm you fetch a lot of data for each run, so MySQL suffers. The change above should help you fix that as well.