Don't stress too much about the logbook...and please do a search on the other threads in the main drama forum. This topic has been addressed many times before.
With the logbook, you have to treat it like a diary and the best logs are written in every time your group catches up, or you have an idea...they should be like a running commentary of your progress...i.e. Today we thought about this...we tried this...we liked/disliked this...etcetc.
It's not HOW much you have in the log, it's what is actually in it. Mind you, with that said markers don't like seeing a log with only 10pages in it.