I've heard between $250-300 a day plus expenses. There aren't too many Part 91 operators that operate on per diem. As far as a duty day, it's all up to the operator. A 14-hour duty day isn't unusual. Some will push it so it all depends on how bad you want to fly for them. Some companies will fly several legs a day, others will depart at 0530LCL, go to XYZ and sit there until 1700LCL, then return home.
Overtime or after mid-night is all in how you negociated your rate. Some may go for paying extra, however, don't forget that your crewing one of the most popular light jets in the world and there are thousands of qualified pilots on the Citation. Search for "contract pilots" on the net and you might find more info on daily rates. As long as your resonable and how many pilots the company you're trying to contract with has available, you should be able to negociate a fair rate....just be realistic.
Remeber this as well, you are WORKING for them. If they provide meals for full time employees, they should also provide meals for you. They should pay all your associated expenses on the road (hotels, meals, etc.). However, getting them to pay for your movie tickets or cab fair to the pub or pay-per-view movies is pushing it IMHO.
Regards,
2000Flyer