Congratulations on making the transition from RCA to custodian laborer 4!
Some things to correct from the above reply - Yes, take the 955, you have 30 days to get your request in (and your office SHOULD send you the form via tracked priority mail due to an APWU grievance settlement...) Retests are every 180 days as of the last contract, but part of that was that open season is supposed to stay open (with some LMOUs overriding, so just get the request done anyway, mark everything but ET11.)
Next is working conditions. Wow, I mean, seriously, you will not believe the mindset difference you'll find in your new job. When a supervisor asks if you can do something, that's not a backhanded order, that's actually a request you can refuse. You've got your 90 days to get through (calendar days, not 90 days worked like it was as an RCA...) so be extremely careful in following all safety rules. Don't injure yourself.
Shoes: Depending on the physical size of your building, expect to get in 5-8 miles of walking in a day. Black non-skid all leather upper shoes. While a uniform isn't required until after you get your clothing allowance, I'd start buying some dark navy work shirts now. Especially if you're not a veteran. The dirty little secret at most plants and BMCs is that you're a target for everyone else's misery. Blending in and looking like you've worked there for years is a major self defense for new custodial hires. Also props like putting all your keys on a carabiner so you 'sound' like a custodian is another good idea.
Odds are you'll skip orientation and go straight into the maintenance safety course; it is reading an inch thick copy paper printed book and taking a test. Be prepared; bring energy drinks, coffee, water, snacks. CTC training will be more death by power point and blow another day, but you'll be able to do more than just recycle or do trash collection routes once that's done.
Biggest cultural difference is breaks. You take them. Every time. You take your lunch every day. Those breaks and lunches were really hard for me to get used to coming from a RCA. You'll use a card to swipe in and out for BT, OL, IL, ET - ask management to help you, which time clocks have your location code, just tell them you were a rural carrier and always did everything on green cards, so never used time clocks. Other custodians should also give you a hand.
The 955 test mentioned above is taken while you're on the clock so long as it can be scheduled during your tour OR if it can't be (hello COVID), talk to management about how you should schedule it/temporary change of schedule to take it while on the clock. You'll go to the BMC, clock in, and at the appropriate time to get there and rest before your test, check out a vehicle and use that to get to and from testing.
A typical tour begins by putting items in your locker/break/lunch room, clocking in at exactly your tour start, meeting for any standups and getting issued route sheets, checking out equipment, and proceeding to route or duty. First break is usually 2 hours after you clock in, lunch is usually 4 hours after you clock in, second break is usually 6 hours after you clock in, return equipment is usually 8 hours after you clock in, and end tour 8.5 hours after you clock in, unless on the over time desired list where you'll probably do 4 days of overtime a week. (Unofficially, that time after equipment check in is kind of a third break.. Culture shock, so much culture shock.)
Welcome to maintenance. You don't have to be crazy to work here, we'll train you... (Psst, remember, you gotta pretend sometimes to hate your job, and when you reply 'living the dream' they'll assume you're being sarcastic, not that you really are compared to life as an RCA. Biggest shock of all? Two days off a week where you can actually make plans to do things, and nothing is so sweet as actually getting a paid day off.)