My turtles have taken anywhere from 5 minutes to 3 weeks to figure out new basking spots. So long as it's easy for them to climb up there and the temperatures are right, I wouldn't worry and just let them figure it out in their own time.
Napoleon - Western Painted Turtle
Apollo - Eastern Box Turtle
Moxie - Painted Turtle Mutt
RIP Hercules
It took Hurley about a week before he even attempted to go up. Give em time, they'll use it.
Dave in NJ
*1 Male RES Hurley 4 yrs old * 3 cats Joe,Jak and Pip * 3 crested geckos Izabella, Lil Lady & Striker (plus 6 baby cresties) * 1 Wife Kristel *