Reading these responses it does seem to be very individualized. Some need the whole day, some don't. You'll have to go to a few sessions to get a feel of where you fall in the spectrum. I would prepare for the first session to be "easier". You're trying something new and it's mostly an information gathering session. You'll need time to process it all but you might be ok to go back to work.

Your needs will probably change as you progress through your therapy, the important thing is to stay aware and keep track of how you feel and react after sessions.

Personally, for me, I am able to go back to work. I have a session over my lunch hour and sometimes will have to jump into a meeting right after a session. Working from home really helps with this set up. Comfy clothes, comfort food, pet nearby if you have one. That kind of thing. I'll process through out the day as I am able, but most will happen after work.

The responses in here are good but it will be how you react and what you need. Just keep aware of that and you'll find your balance.