sometimes designer need to do a lot of guess working with the client with unclear specification about the design they want.In this situation, we have to research client's industry and other websites with similar products and then need to give sample layout. SO how much time do you spend after this guess work?
5-10 minutes , as a designer you should already be familiar with most industries and get to work ASAP .
I spend time with the client (that the client pays for) to determine exactly what he wants, then put exactly those terms in the contract. Since the batteries on my mind reading device died I've stopped reading any mind but my own. Guess is a clothing manufacturer, not a programming paradigm. (I don't need clients who cost more than they pay.)
I'm with Rukbat, after a lot of wasted time in the past, if it doesn't go in the contract, it doesn't get done (without an extra charge).