UPDATE...
I followed Grog's suggestion to flash the Zgemma H.2H box with bare OpenATV 6.4 to see how long that takes to boot up from power off, and now present the following 3 Test Results:
TEST 1. Flash Zgemma H.2H box with OpenATV 6.4.
1. Copied latest OpenATV 6.4 from Nightly Downloads onto 2GB USB Drive
2. Inserted USB Drive in rear slot
3. Turned on rear white power switch while depressing front silver power switch
4. Front display shows BOOT, then USB
5. When USB shows, released front silver power switch
6. Front display shows FLSH... after a minute changes to BOOT with red LED...
7. After 30 minutes, display changes to BOOT with green LED, and boots up from -0- to -49-
8. Then I set up box with OpenATV only, on Astra2 28.2E channels etc.
9. When fully set up, powered off box and left overnight for 10 hours.
TEST 2. Turned on same 'cold' Zgemma H.2H box from power off.
1. Display shows BOOT with red LED...
2. After 30 minutes display changes to BOOT with green LED, and fully boots up from -0- to -100-
3. Turned off 'warm' box (and immediately switched it on again for Test 3).
TEST 3. Turned on same 'warm' Zgemma H.2H box from power off.
1. Display shows BOOT with red LED...
2. After 30 minutes display changes to BOOT with green LED, and fully boots up from -0- to -100-
Above 3 Tests show the box always needs 30 minutes to boot up from power off, and when left powered on it works normally.