People at the firm will help you if you have a good attitude coming in as post-MBA Associate. Being intellectually curious is important and try to understand the big picture (e.g., why does it make sense for two cos to merge, why not another co, what are the other strategic options, etc.).
Many banks require MBA Associates to do analyst work for the first 6 - 12 months on the job, while most likely an experienced analyst checks your work. It's a little odd dynamic being older and senior but "reporting" to the 2nd or 3rd year analyst, so it's pretty important to keep your ego in check. If you're an easy going person and don't act like you're better than the analysts, you'll generally find analysts to be pretty open to helping out and frankly sharing the work load (though you may just end up working with some analyst that's on his or her way out and doesn't want to be helpful regardless). By the way, this doesn't mean the analyst doesn't do any work, but the Associate is much more hands on. Ideally you'd split up work ("I'll take slides 1-15, you take 16-30, I'm going to do the model would you mind checking it after to make sure I'm doing it correctly since you have more experience?"). You'll kind of have to concede that you're just not going to be "above" the 2nd or 3rd year analyst class when you first join the firm, but that's okay because most likely they're leaving or if they're going to be promoted you won't be managing them anyway.
Even if your bank doesn't require Associates to do analyst work, I would highly highly suggest you volunteering to at the very least, split up the work on putting together slides and definitely spend a significant amount of time doing the actual modeling. It's much easier to gain the respect of future analysts and "manage" them later on when (a) you actually know what the hell you're doing, and (b) willing to at least do some work so everyone goes home a little earlier. It's pretty amazing how quickly an Associate can lose the respect of even 1st year analyst if he/she has a reputation for being incompetent technically, incredibly slow in ppt/excel, or goes home early every day while the analyst stays past midnight because he/she is doing everything. It's fine if you're going home maybe an hour or two before the Analyst, but there shouldn't be a consistent theme where you're clocking out at 6pm and the Analyst leaves at 2am. I frankly believe it's not until you're a 3rd year Associate or higher where you're truly just checking work and outlining slides, rather than actually doing them.
As a side, it does help that by the time you've finished your MBA courses, study online guides, completed interviews, plus depending on the bank Training the Street prior to starting, you'll have at least a decent foundation to pick things up pretty quickly since they're pretty relevant to the job itself - unlike Audit, where basic accounting is necessary but not that relevant to performing the job itself.
I think you'll find that transitioning from Big 4 to banking to be easier (skill/knowledge wise not hours) than you anticipate. For sure there's a massive learning curve, but fundamental understanding of the financial statements and accounting, and just general exposure to businesses is incredible helpful as you ramp up the learning curve. Most analysts or associates that came from Big 4 audit or TAS picked things up pretty quickly, as long as they somehow made their way into a banking position.
If you're a post mba associate, you need to earn the respect of your analyst and VP and the only way to do that is to effectively do analyst work in the first 6 to 10 months on the job and get a solid technical base. You should definitely try and act like an associate during this time though ie. chime in on calls and try to drive processes forward. I wouldn't take orders from an experienced analyst but realize that if you are doing something like modeling, the second or third year analyst can run circles around you so you should definitely learn from them and take direction on that at times.
If you come in and try bossing around analysts without knowing how to do a task yourself, there will be conflicts and a possible blow up. A second year analyst that knows a lot more than you and is leaving the firm in a couple months is not going to take your bs if he doesn't respect you. Work hard and win his/her respect, and they will make your life easier.