I'm also an auditor for a big 4, similar to Astou. We do have busier times in which the traditional 40 hour work week may increase to 55-70 hour weeks. With that said, the firm does a really great job at promoting flexibility to complement those busier times.
If you look to industry, your schedule is likely to more closely mirror the traditional 40 hour work week, with the exception of having a couple busy days every month for when books close.
As for a typical day in the life - I'm at a senior level and 90% of the time I spend my days on site at the client. Our team works from here and my day can consist of working in our internal system on our audit workpapers, discussions with the client, and maintaining team oversight. The atmosphere for me is very team-oriented; however, teams will range in size depending on the client.
As you work to decide your next steps, I would first take consideration as to what you want your daily routine to look like and allow the answers within to guide you in the direction that best suites what you're looking for.