to 1 mm is the total recommended thickness for the coating. When you apply by rolling the coating , it means 2 thick coats ( low pressure on the roller). The second coat can either be applied when the first one is dry to the touch or anytime after that. There is no advantage one over the other but when leaving the first coat to dry longer (couple of days , weeks or even months) make sure that  it stays clean to assure maximum adhesion.