I love flexi rod sets. To maintain them at night, I:
Fold my large silk scarf in a triangle shape.
Flip my head upside down so that all the curls are falling towards the floor
Tie the scarf so that the open part at the top has the curls sticking out
Sit upright then stuff the exposed curls back into the top of the scarf
My flexi rod sets usually last anywhere from 10-14 days. I can only wear it down for a good 3-4 of those days. The back curls stretch out a little too much for my liking so the rest of the time I'll do an updo. My favs are a high pony with faux bangs or a faux inverted bob.