This is a very complicated question in fact because it all depends of what time in war you're talking about, which induces what sensors and what skill have the opposition...
I guess we all learned through hard experiences that your watch crew always spot targets too late (you can see them with the binos a long time before crew reports them) and of course the DDs always spot you too early.
A very clear and calm night if 2 or more escorts is for me a no go, not talking about a clear day.
I like a little bad weather, makes attack a bit more difficult but getting away much easier (which is usually the part where you risk to get killed).
Two things have influence on how they visually detect you : your profile and your speed.
From what you write I think you're doing the right things, just needs practice.
If you do the intercept right and are at meeting point a little early, get a hydrophone fix, surface and go towards the contact. As soon as you can see them it's time to put yourself on their path, submerge and wait. Hydrophone and a short periscope peek from time to time should put you in position.