I think spending 2 days to get it right is just fine, I have often spent longer (and I mean MUCH longer!!!). For me alot depents on how much the client is involved. As design is based TOTALLY on opinion the old saying "How long is a peice of string" comes to mind. Don't forget, that if you don't bill them you won't get the money. If in doubt Charge More, they may notice, and argue, and then, you may reduce.
Thanks In Advance