Been mostly lurking on this site but wanted to reply to this.
With HHN casting you can be cast as a Reserve and work the event more causally, only a few nights a week. Last year Reserves I believe had to work 10 specific event nights and could work more if they wanted but didn't have to, this is nice if you want to try out different roles, have other obligations and can't work HHN 40+ hours a week, it's intense so you have to be mentally and physically prepared for that. You can be hard-cast which can happen either during auditions or during the event if someone drops out of a hard-cast role (hard-cast means your a specific character for the entire event and work the event every single night). You don't get out until 1 or 2am most nights (especially during the second half of the event when it tends to run later), last year with the ST house I believe those casts were there until 3 or 4am some nights due to the long lines. You're in-time is around 5pm, depending on what cast you're on. If you request too many days off and go to audition they will either stick you in Reserve or not hire you at all. If you want to be hard-cast (assuming they have a role they feel you'd be perfect for) then you need almost full availability (the less time off you request the better).
I hope you get to do it, it's an absolute blast and something I think everyone who loves the event should try and do at least once.