I generally start at the bottom - Luciaphil - and check to see if there's anything new. For quite a while there hasn't been, but these last few days, it's suddenly been revived! Then, I go to Robservations. I usually skim that really quickly, as I've already seen the episode, and mostly read the comments and any replies.
Then, I check out anything new in Testing - that's usually pretty quick.
Finally, I arrive at the Main Forum - do a quick check to see how many topics have new items and then search for the new posts. I like it when there are a lot of replies to a few topics rather than a lot of topics with 1 or 2 posts, as, once in a thread, it's easy to read quickly and move down the page, rather than waiting for each topic to come up.
I do a lot of skimming. Many items are short or occasionally something that I don't know much about and read very quickly. Once in a while there's a more in-depth item that does require real reading.
I generally try not to post too many things myself (especially if it's a really busy day and I'm signing on even later than usual). If there's a birthday or something that requires a more creative response, I try to find something that will look colorful, but be simple to create.
I suppose I get through it in less than an hour. If it's a day with more time, I come a bit earlier and then check back later for anything new (like now!)