I'm very much still finding my feet on the exposure and timings. Going try some multigrade paper next as I have the Meograde head that does density and conrast. All guesswork mind you at this stage.
The good thing with multicontrast heads is that they automatically compensate in order to even-out the exposure when you change contrast. Something I don't have the luxury of.
But for the basic exposure, things are much easier than you think. You just have to think in f/stops. Ever since I started doing so, I cut my testing time in more than half!
First thing you'll notice: if you used an exposure meter, your exposures on the film will be incredibly even from one frame to the next. That means that once you get the proper exposure for one print, all the other ones will be in the same ballpark for the size you enlarge. So if you do everything on 5x7, the exposures will be pretty close.
Also, I use a fixed aperture and adjust the exposure time in stop increments. This is where the secret lies. The "adding a few seconds" method does not work.
What I do is usually either do an f/stop based test strip or simply print a section of the image on a strip using an exposure time I know will give me a result. Then, I look at the developed strip and ask myself how many stops darker or lighter I want it to be. Then just multiply or divide the time by 2 the number of stops you want. That simple.
Takes a while to get used to it but it works flawlessly (even when doing dodging and burning operations).