Thinning the initial coats with mineral spirits WILL be absorbed a little deeper (wood cell structure does that by capillary action) and has the added benefit of drying the application a bit faster to allow subsequent coats sooner.
Actual testing over many years with many different finishes shows both assumptions to be wrong. The mineral spirits outruns the finish and goes deeper, but the finish does not. In most cases it reduces the finish penetration. It also slows curing of oil finishes rather than speeding them up.
Also, in some non-oil finishes, like epoxies, mineral spirits and acetone will create pores through the finish as the solvents leave, greatly reducing waterproofing.
To test drying speed make two sample cubes and weigh them on a powder scale. Finish them two different ways and monitor their weights... very quick and easy test and then you can prove it for yourself. Penetration is easy to prove by the method I posted earlier.
Good oil with driers will cure very fast... several coats per day is usually possible.
