A lot of people don’t realize that they really should be using a 20A timer. The regular ones are really meant more for table lamps.
Most circuits that people use for home growing are only 15A. A 20A timer should have a different electrical pin out than a 15A or less unit, the neutral prong should be "T" shaped. This prevents someone from plugging 20A devices into a 15A circuit. Most timers are rated for 10-12A from what I've found. A 1000W HID is 8.33A.