What do you do in them 5 hours??
Take your money!
People, schools and aeroplanes do differ but I am not sure why they think that people require five hours to convert from a 172/cherokee to an arrow type machine.
Nominally takes 7 to get a twin rating, and that requires a bit more hard work than retracting the gear and wobbling the prop.
As Keygrip says you have done the differences training by doing your MEP if it was a 'conventional' twin with retractable gear and VP prop. If they want you to do some dual in their single to familiarise yourself with it and they with you, fair enough. Not five hours though.