Turn around time for me depends on the individual job and how busy I already am, a week to two weeks is my usual quote. But as a general rule, I estimate how long it’s going to take me based on previous jobs (factoring things like set up and clean up time and how many prints I can do on average in an hour, time its going to take to make plates and wither I have the paper on hand of if it will need to be ordered etc.) and then I double it. That way if something goes wrong, I get a migraine or my kid gets sick I don’t miss the deadline. If you get it done before you said you would the client will not complain but they certainly will if you miss the deadline. For wedding jobs it can be helpful to do the envelopes first, that way they can begin addressing them while you finish off the rest of the order. Also I am clear with the client that the clock doesn’t start until the final design has been approved, which often helps to speed things up.