I have experienced no issues due to running these extended periods.
Like a PC that runs 24/7, you may need to clean the inside a bit more often and perhaps the fans may need replacement sooner. But keeping it clean inside will help.
I use compressed air from an eight gallon DeWalt compressor together with an OSHA approved air nozzle. Set the output pressure for ~40 lbs/sq.in then regulate the air pressure to sensitive cabinet areas by backing off a bit on the nozzle distance. Don't use any imported air nozzle. The OSHA nozzles have a pair of openings at right angles to the main air outlet. If the outlet is obstructed for any reason, the side openings will safely port the air out.
Cover removal is easy on the Flex 6000 series. But before you do, purchase a Torx T8 x 60mm hand wrench. You'll need it to remove the cabinet screws. I really like Flex's choice of Torx hardware. It's almost impossible to mar the screw heads since the Torx uses a positive drive head with no means for slippage.
After playing with the numbers for a while it came out that here in NC it would cost about $18/year to run my 6500 24/7. add a few dollars for the times when the rig is actually being used. I think I will run 24/7 from now on.
I think I need to get a life :)