Vittoria Corsa Evo CX tubulars: overnight, quite a bit. My experience is the same as yours.
Tufo S 33 Pro tubulars: takes about a month to go from 130psi to 100psi
With tubulars, it could be the tubes, but it could also be the valve cores. Most are removable, and many leak.
All my clinchers: 10psi/day for 2-3 days, bottoming out at 40psi in about a week or so, some slower than others.