This is from what I know about CRT manufacture. A 35 / 36 / 38 " tube will achieve very near 29.9 In / hg within 3 / 4 minutes while pulling through a glass tube about 8 mm ID. To get down to CRT vac levels, it takes 4 hours while baking the tube in an oven to get the last few molecules out. This is a level that no one would ever be able to attain in an AC system.

A standard automotive ac system has a fixed volume that really isn't that large. Sure, in the first two minutes a larger hose may offer greater flow, however as the vac reading gets larger, there is less flow through the valve. When you hit anything near 20 in / hg , flow is minimal since there isn't much air in there. Time under vacuum is important to allow moisture to boil off.

On a vehicle with dual AC / bus or large commercial system, larger ports would help but that is beyond the scope of what we are trying to do.