The default for the screen on the FR965 either turning off or going into low power mode for the AOD is 8 seconds. You can change it under System / Display / General Use. For watch faces built in to the unit this works fine and you can set it to 4, 8, or 15 sec. However, for watch faces downloaded from Connect IQ (even ones made by Garmin) the maximum time they are on is 8 sec. Changing the value to 15 sec has no effect. You can reduce the time to 4 sec and that works. However, increasing to 15 sec only has the display on for 8 sec. My FR965 is running the latest OS 4.19.
Try it and see if it behaves like that for you. Is this a bug?