If they want to add a lengthy cooldown to mounts they need to put gathering nodes a heck of a lot closer together or remove the slow walk and still allow sprinting in stealth mode.

Outside that I don't see an issue. The mount cast time is what .5 to 1 second? It's fine as is imo and I like the freedom to jump on and off as I please. Adding a cooldown, esp one as lengthy as a full minute would be nothing but infuriating.