Man,a startup(coding in the begining,...) is like a marathon.if you work 8 hours/day with quality and focus it's enough if you can continue.
Working 15 hours/days and being sleep deprivated will leave you burn out.A good sleep is necessary for a good work.
it's oki to be impatient with the small steps ,but be careful with your health(the long term)that will help you finish the marathon