No day is ever typical ( I just wanted to be the first one to say that.) That said, there are some very similar days. Depending on the level of client you are more or less their underpaid and unappreciated slave. Generally the most intense days are setup days. It's best when the engineer gives you an input list and you can just set up the studio with the rest of the staff before the client/s arrive. Other times musicians pour into the studio without letting you know anything in advance you and 2-4 others setup for four hours, then track for another 12 and when you present the log to be signed at the end of the day the client says what do you mean 16 hours we didn't start recording until xx o clock. Setup days are also the most fun, you haul ass and know the meaning of action and at the end of the day the studio is making music. Then you have just regular old work days, as a studio owner these were my favorite as I didn't really have to do anything but put in an occasional appearance. These days generally run 8-12 hours. Lots of button pushing, knob turning and instrument tuning. Copious notes should be taken and the one useful thing about a dat machine is that you can run a dat the whole time incase any good surprises/happy accidents should occur. Some days had two different sessions so at around midnight there would be a changeover where the second engineer or the incoming engineer would change the patch and recall the console then sit down for his 8-12 hour button pushing knob turning and instrument tuning shift. What seemed like the suckiest days to me were the ending days. Mostly people want to accomplish more in the studio than they have budgetted the time for. So toward the end on the last night everything starts getting tight and stressful ( the bad stress, setup days are usually the good stress). Then when the session is finally over the engineer usually has another four hours or so of housekeeping where he does backups, makes CD's logs tapes does all kinds of tedious tasks when he would rather go home to bed.
Sometimes the clients want to do drugs, then the sessions last longer and less gets done, especially if they succeed in talking the engineer into getting high with them. Othertimes you don't have enoough work and end up trying to setup, record and breakdown in a day and then the client wonders why they don't have a mixed product at the end. After all they can play their whole set in an hour! Then when all is said and done you get maybe 6000 bucks for a month of work and the record you killed yourself for actually goes platinum, the producer get a million bucks the artist gets a million bucks the boutique label gets a few million, the distributor gets the rest and they didn't put your name on it, so you barely manage to up your day rate.
Have fun and enjoy making great music, cause you aren't in th business for your health, and you certainly aren't in it for the money.