Sure its ok. Some people may say to run them up and down once in awhile to help keep the system healthy, but it's not clear what that does beside wiping the ram against the seals. Wiping the ram clean before retracting seems a more helpful thing to do, especially if in an environment where salt or dirt can collect on them.
We routinely leave ours on the jacks for extended periods.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL