We did both Ferrari musuems and Pagani last year - see here-
Pagani, you only need to allow a few hours unless you book the factory tour in advance.
We did both Ferrari musuems easily in a day. (seperate locations- Modena and Maranello, about 20km apart) - you can buy the tickets together from their website.
We didn't go in the Lamborghini museum, just parked outside on our way out of Modena as we'd got a long drive ahead. A car friend who's visited suggests it's not as good as ferarri given they've not got the same racing pedigree as Ferarri etc.
We'd not be driving that far into Italy again! too hot, poor roads, traffic etc. The dolomites and around Lake Garda is much better in a Westie.
We didn't actually drive from Modena to Ferarri due to traffic and very wet weather, so missed the opportunity of a photo outside the Ferarri factory etc.