It comes down to how you quoted the job. I always specify in a quote the regular hours for my crews to ensure that if we encounter locked premises, due to failure of the client to ensure access, that we can still bill for the on-site hours. If atypical hours are requested, I call those out in detail to ensure proper access expectations. I also do so to ensure that I use the correct shift rates in my quote. If you quoted for after regular hours install (perhaps to minimize disruption to daytime operations of the client), then after hours is after hours. Hopefully you allowed for 3rd shift premiums.
Is it normal ? Well, yes. Not common, but still normal.
Would you accommodate this ? As long as what the client asks is not unethical, illegal, or in disregard of safety regs, then of course, YES. The client will be quoted, and have to pay, a premium for their special requests ... but that is how you make customer service work and score a profitable job.