Clutch,
You are a man of many questions! A full dose later in the same day is not necessarily recommended, but won't be harmful. I'd give at least 5-6 hours time between however. Taking 2 full doses/day in my opinion, will be a waste of money, long term.
17-HD works for some as an effective stimulant, but there is nothing there that will accomplish anything else. There's a thread on BBcom that details a breakdown of the ingredients and actually shows it will be detrimental to long term muscle gains. If you get some RPM, I'd completely drop 17-HD and never waste another dime on it. Note: Further proof it's junk: Vyotech won't tell you a single damned scientific piece of evidence to back the product, let alone answer questions at all on it.
Drink plenty of water, and you will have no issues with cramping. Muscle hardening does not refer to cramping.... it refers to denser muscle feel.