If they are paying you to work on-site, then it makes sense for them to have some say in when that happens, or you might as well have been working remotely. It'

If they are paying you to work on-site, then it makes sense for them to have some say in when that happens, or you might as well have been working remotely. It's hard to fault them for wanting to let their own team get a chance to understand the tech, so your project does not become yet another "PoS left by some consultant" that nobody wants to touch. I'd suggest seeing if perhaps you can reach a compromise where you retain some flexibility, but there's a bunch of your hours that are sure to overlap with the office hours (e.g. always be on-site for 3-4 hours around noon). And maybe you'd even only have to do this part of the week, e.g. mon-wed-fri? With most conflicts, the solution is usually to have both parties answer the question "what are you trying to achieve?" and then working together to find a third solution that satisfies both parties, instead of focusing too much on the schism between the two proposed solutions that the parties had come up with individually. If all this is a big hassle for you then by all means, charge accordingly, and in the future think more about what kinds of gigs you take on and how much face time they are likely to require. Maybe 'remote only' is a better fit for you?