How long does it take to hike up and down Kobe Nunobiki Herb Garden?

I'm terrified of cable cars, so my only way to experience this spot would be on foot. I also think I'd enjoy it more that way, but I only have a day in Kobe and would like to be able to enjoy Kitano Ijinkan-Gai and visit the Earthquake Memorial Museum as well.

Any tips? Should I just skip the gardens and seek nature during other stops during this trip?