Once a day, near the start of day is best. Take advantage of the blood flow, and post girth routine with expansion exercises.
Use the restricted rate of 5 minutes from erection blood flow volume (100%) to 50% (flaccid state). This allows the blood to slowly flow out, keeping the expansion constant. If the penis goes cold or the blood becomes purple-ish, time the restrictive rate from 5 minutes to 3 minutes. To refresh the blood volume again, discretely get and erection to pump fresh blood back into the penis.
Purple penis color, don't allow it. Silicone
strap, medical rubber band used for blood drawing, hair ties, flexible bandage, and the list goes on. Get one that beat suits your needs.