At least 1mg but no more than 3mg is the right dosage. Helps go to sleep quicker but doesn't always improve overall night sleep. Also handy to take in order to go to sleep again when waking up in the middle of the night, provided you still have at least 3 to 4 hours sleeping time ahead, otherwise you could wake up drowsy.
Pharmacies in Thailand sell the delayed onset tablets at a hefty price. I found the delayed onset tablets not to be useful.