Well, generally speaking, a delay is highly dependent on your BPM, for delay time anyway. So depending on your tempo, you'd have to calculate 60000/your BPM to get the exact delay time settings.
As for delay feedback, that's honestly up to taste. I just leave the feedback so that I get like two, maximum 3 repetitions of a note. But again, it's up to you.
That's how I approach delay in general for my guitar tones.