My suggestion would be a 10 second timer, restoring an amount equal to resting at a shrine with the same heal (or repair) skill, plus whatever bonus the kit grants. Put a 1 minute cooldown on it, and with an interuptable 10 second cast and the "tie shoes" animation, it's not going to be viable for combat healing.
Along with this, I'd double the speed (halve the time) of wholeness of body. And buff paladins and rangers. Seriously, they need it.