I think exposure is different with everyone depending on what you can handle.
My therapist has me watching videos/reading articles on atheism 3 nights a week for 1 hour each night (b/c I was scared God and all that goes with it wasn't real). But I couldn't handle it and had to stop earlier than 1hr because my anxiety got so high I would get panic attacks. So he told me to do it every night for only 20 minutes to start with then add 2 extra minutes every night until I got to 1 hour then go back to 3 nights per week.
He also has me not going online (google, christian sights, etc) looking for reassurance to my questions. That was hard for me also. I couldn't do it for the first week very well, but each day I started to taper off from looking for reassurance more and more and ever since then I rarely go online for it, and my anxiety has gone down.
He also told me I can only ask actual people for reassurance to my questions, but I can only ask 3 times per week and it has to be a different question and a different person each time.
And the last things he has me doing is to make up extremely exaggerated scenarios in my mind about my thoughts, like, "There is no God so I am going to barge into church on Sunday and take everyone hostage and tell them if they don't believe me they will all die and go to hell", which pretty much makes no sense b/c if there is no God then there is no hell, and of course b/c I would never really do those things, Lol. I told him that the thoughts make me feel like I'm doing something so wrong, but I do them anyways and they work. He told me to do them every hour, but I forget, so he said at least do them every time I have thoughts and get anxious.
Anyways, I also journal everything and write down my anxiety (especially before and after my homework), and tell the therapist everything when I see him again.
I have to tell you though, I have not had much anxiety (unless I'm doing my homework, but it goes away very quickly now and doesn't get as bad) since I've been facing these things.
It sounds like a lot, and on days where I don't have anxiety anymore I sometimes forget to do the homework, but I try to keep up with it. It is pretty much me facing my fears of no God and becoming an atheist.
I also have thoughts that I'm not doing the "right" thing for God or He's not happy with me and stuff like that, but my therapist said we will deal with all that later. One thing at a time. I am actually loving my life again, (at least most of the time).