Clinicals should be held at the times and dates that they were posted as at registration barring some sort of very special circumstance (ie hospital decides to change time, natural disaster, emergencies, etc). Starting clinicals 2 hours late because your instructor has tennis lessons, or holding them on tuesday instead of wednesday because her daughter is home from college is not acceptable.
Re: Pre and Post clinical...define "okay". It's not against the rules to not have a pre or post clinical. Is it the best practice? No. But then again, many teachers are not the best either, and truth be told, I've had some pre and post clinicals that were rather pointless and a waste of time.
Yes, I do agree wholeheartedly that pre and post clinicals is where much of the learning goes on (talking about the rationale behind protocol and procedures, discussing lab values, how to improve on patient care that was offered, etc). And if you feel like you are missing out on this experience, then by all means speak to someone, because you're paying (good money-I'm sure) for your education, and you only go through nursing school once--hopefully--so really you're entitled to voice your opinion.
ETA: Not to be too blunt, but instead of tip toe-ing around it and using pseudo-hypotheticals, why not just come out and say what the exact situation is, that way we can better judge. It'd give more insight.
Pardon my spelling
and grammatical errors, as I'm on my 4th night in a row (third 12 hour shift).