This depend on the price action of each coins and the target profit, in my experience duration when buy and sell in day trading can be around 2 days , but if the price stay stagnan the duration can be longer. At the moment my target profit for every trade is 10% and stop loss 5%, and the price can be reached the target or the stop loss around 1 to 3 days.
The best time period in a day is that when you free and no other work to do. You can spend that time for bitcoin trading, because when are mentally free you will better focus on trading and will make good and right decisions on the right time. Right decision on the right time will give you profit eventually. Do not set in front of your computer in time of depression.
Yes, you are the right answer, however, you want to practice each time frame with indicator or tools and after that, you select one of the time frames on which you are confident. There is the best time frame which would useful to you day trading 5mins, 15 mins, and 30 mins. Trading Cryptocurrency Bitcoin, Ethereum, Ripple trade popular.