In my company SYS and ENG are checked on the ground to check HYD QTY (minimum 76% and no RF indication) and ENG OIL quantity (minimum 12 liters) for pre-flight and we’ll record these into the tech log at the beginning of every flight. Then, still on the ground, we’ll use the ENG page for engine start.
After pushback with engines stabilized idle the lower DU will be blanked right before we read the before taxi checklist. While it’s not necessary as per SOPs, some people (including myself) like to select the SYS page during flap extension and flight controls check to make sure the hydraulic qty and pressure stay coherent with having extended flaps and used full range of motion on the controls (HYD A qty will be lower with gear extended and HYD B qty will be lower with flaps extended). I could be wrong but my reasoning is that if a Hydraulic line was ready to pop, the full range flight controls check would make it happen. A full range flight control check has to be done smoothly and slowly. Remember it’s 3000psi you’re working with. I’ve seen a hydraulic leak during a walkaround. Corrosive skydrol fluid raining down from the wheel well. Interesting sight.
Any exceedance during the rest of the flight will automatically make lower DU pop back on. If at any time during the flight you’re curious about any of the indications in either the ENG or SYS screen, you can turn it on but make sure to blank it again after you’ve looked. That way the popup feature will be available again. During take off it must be blanked.
If at any time someone forgets to blank the lower DU in flight, the colleague will go “Hey, did you leave this on or did it pop-up?”.