It differs from person to person, actually. The most "common" times to take ephedrine HCL would be 3 times a day, once in the early morning, once before lunch, and once in the mid-afternoon. Ideally each dosage should come before a meal or exercise and never surpass 100mg ephedrine HCL on any given day
I taken the ECA stack for some years (on and off of course). Try taking it early morning, mid morning and around 1:30. This should allow time for it to exit the system for natural sleep to occur.