The first advice to you, is to do the right thing at the beginning, otherwise you will suffer by the compromises forever..!! The right thing, in my opinion, is to have the sterile preparations as long as -out of the 24 hours- as possible.
However, here are some compromises if not 24 hours:
Some of these preparations can be done as batches, for example the TPN, and large volume parenteral solutions, you can make standardized preparations and keep them at the ward fridge. Some of the antibiotic/antifungals/IV preparations can be also done in the same way.
You can put also a laminar flow hood inside a segregated room at the hospital (as mentioned on USP 797), so you can prepare low risk preparations with BUD of 12 hours. You may let one on-call pharmacist (or more according to your production scale) to come to the hospital (if pharmacy is closed), so he/she can prepare the queue of medications which couldn’t be batched.
For STAT medications, it is not possible to cover them all if you don’t have 24 hour service. As for the USP 797, if low risk medications are prepared under non-sterile conditions, it can be used within one hour after preparing. But, again, it is still risky to standardize such a practice, and a nurse who will be the one who prepares them..!!
Keep in mind that all the above have much material and time wasting, which will raise the costs at your hospital, so I would better use this point to convince your administration to allow a 24 hour service, at least for some of the IV preparations.