I always schedule 2 full days for Rules. Depends how much of a stickler your LOM is but you could be asked more or less anything in the Rule Book. Certainly everything in TS1, whichever of the signalling modules you work (TS2/TS3/TS4/TS5/TS7/TS8), TS9 if you have level crossings, TS11, T3, S5, S7, P1/P2, M1/M2/M3, TW7 and the NOI. I always cover at least one thing from each module and many I go through entirely. If it is clear someone has good knowledge then I move on to another topic, if they are a bit vague then I probe deeper. Your LOM will let whoever is doing verification know what you are good at and what you are shaky on so expect to be asked about anything you were not up to scratch on the first time round. Otherwise the verification will probably just cover high risk stuff like Line Blockages, passing signals at danger etc.. Verification is usually just an hour or two. Expect the OM to give you some words of wisdom at the end.
Remember your LOM and OM want you to pass! You need to put the work in though and revise. Also try to keep your rules knowledge up to date once you're passed out.