Man, me and my body would love to do a full detail in 3-4 hours! They only way to get quicker is have your stuff ready and have the proper tools to do the job. There was a topic around about how long it takes for a good wash, I think most were around the two hour mark, that leaves you 2 hours to work the paint and do an interior. It takes me about 2 hours for a complete interior. So in your time I have done zero paint work. A full interior for me is about 8-10 hours with my GF helping on the interior. Full for me is a wash, decon mild cut and polish. Interior vac, shampoo and wipe of all materials. Leather gets cleaned and conditioned.