|My question:Can the laser pointer be on 24h/day? Any suggestions?

A laser pointer probably isn't the best method for sensing motion.
For detecting speed, you might be better off with a pre-made photo-
beam assembly.  One common type is a U-shaped gizmo with an IR led
and an IR photo-transistor pre-aligned and pre-focused on either
side of the slot.  If you can have another wheel on the same shaft
as the "real" one and have the edge of that smaller wheel sit in
the sensor's gap, then you should be able to easily and reliably
detect the wheel's rotation.