I think it would be to hard to round it off to the minute. However, you could do that and use myhours.com and livetimer.com. Both of these online programs I found from other VA from this website.

Another option you can do is set a block of time everyday and bill in 15 min cycles. From 9:00 to 9:15, 12:30 to 12:45, 4:00 to 4:15. etc. There will be some days when you won't have any emails and some days it may be heavy. But should balance out thru the month.

I think you did the right thing by getting your foot in the door and this will be a great learning curve. I have a client that I use as a test client, so the rate is really low but the feed back is very helpful.

Good luck and let me know how it works

Julian