One of the most popular questions on this forum, whether it's for firm comparisons, rankings (ugh), or general information, is one that asks about the hours of a firm. The question is legitimate and important to ask; the answers that are thrown around, however, are not always that helpful.
The truth is, if you work at a reputable bank with deal flow, you will work banking hours, which means an ebb and flow of 55-100 hour work weeks depending on a couple of factors:
Are you on a mega-merger with exploding deadlines? Yeah, you might have a 100/hr week(s). Starting out on a sell-side process for a smaller firm? Things might be chill if the firm drags their feet and you can get out by 7pm on Friday to make your dinner plans. Building a pitch deck? This one will depend on how much your MD loves to give comments and how good your associate is at translating these comments. What type of deal you're on, how many people are on the deal, what your MD is like, your team's work flow and organization - these factors cause a drastic variation in hours, a variation that is seen in all banks. Banks don't have an "hours average" target that they try to hit.
The Deal Flow
Zooming out of the dynamics of an individual deal, if there's a lot going on with your firm, you're more likely to get worked harder. In slower months such as the summers where all the execs want to be lounging in the hamptons, things will get slower. This also varies depending on the group you're in and the macroeconomic environment (hello coronavirus). Once again you see variation.
So this is one of the reasons why the average hours per week per bank tends to be different across the banks. Note that culture is more than just work/life balance but nonetheless plays an important role. Are you at a bank with a heavy facetime culture or one where people are big on the workaholic competition (who can work more hours?) culture? Yeah, expect more hours on average. Do most people in the bank get in late, leave early on Fridays, no facetime, etc.? You can expect fewer hours on average. Individuals who are senior to you can respect your work/life balance out of individual personalities, but if the firm culture compels the majority of seniors to give you a life, you'll have better hours on average. I won't name banks, but across my friends and myself, EBs tend to be better in the culture front (but even this is wrong as you can't classify all EBs as an identical group) than BBs. Did I mention that intragroup and intrateam culture matters too? No one on WSO is gonna out themselves this specifically, so save for hearsay, you won't get a great view on this.
But again, this is on average. Pulling a ton of hours at a place with good culture? See #1 and #2.
No one really talks about this but it's honestly one of the most important determinants. How ambitious are you? How hardworking? How much do you like your job? You can do the minimal level of work as an analyst, do what your seniors tell you, and clock out. You can pass on the harder staffings (depending on your staffing process), go into a group with lesser deal flow, and coast (this is a relative term) to get better hours. If you're hungrier, take time to synthesize through the information on every deal, do good work and voluntarily take on big deals, yeah you'll work more.
Last note pertaining to the self is your reputation, which is a function of the above. If you're seen as a lazier worker you'll find that you'll be put on shittier deals, but if your reputation is stellar you might get rogue staffed on the next huge deal because your seniors enjoy working with you and can trust you. Over time as your rapport begins to develop with your deal team members and seniors, you might find fewer hours from the refined work process you've developed, or more hours because they trust you with more responsibilities.
TLDR: While it is true that some firms may demand fewer / more hours than others on average, the truth about banking is that your hours will sometimes be awful, sometimes be okay, mostly be somewhere inbetween, but will never be amazing. There's an incredible amount of variation and that's what you should expect. As a result, comparing hours between firms is not an incredibly productive task, as you'll likely reach both spectrums throughout your two years. Focus on what'll make you enjoy those hours.