Hi there,
I'm using FF to chart my BBT's too and just getting used to it. This is my 2nd month and it's really interesting to have 2 months to compare.
"Drinking" refers to alcohol and not just any fluids as alcohol for most people will cause their temps to fluctuate (usually rise). If you tick the box for drinking when you have a few bevvies, FF will take this into account when reading your chart, so it's worth putting the info in. I had 3 half glasses of Guinness last night and my temp is up a little from the last 6 days, so it could be the alcohol that has done that.
As for time differences, I take mine at 0805 hrs any morning that I can, but because I work a rolling shift pattern, this coming week I will have to chart in the afternoon when I wake up after nights. There is some info on FF about shift workers and it recommends that you take your temp on these days after at least 3 hours of consistent sleep. It shows up on the chart as an OPEN blue dot as opposed to the other CLOSED blue dots. However, although it makes the chart more difficult to read, I found it fine last month and still got a good overall indication of what's going on during my cycle. I got a reading on my ovulation too, which shows that it didn't make that much difference at all. Therefore, if I were you, I wouldn't worry about your weekends being slightly different by hours, just as long as you take them after a long period of sleep.
Good luck with it.