Stat regen is near 50 seconds with passives from the alchemy line. 47 sec iirc except for one specific formulation for the tri stat pot extends health regen a little bit longer.

Secondary effects like Immovable have a significantly shorter duration and always have. Immovable for 50 seconds is probably a little OP. Also, think about the detect potion. Preventing someone from going into stealth for 50 seconds, even half that, is probably a little much.

You need to look at the duration for each item in a potion.