From what we can see, where an employee has truly resigned from a full-time position and then asked to be re-hired on a part-time basis, it would be deemed two separate employments. The only notice requirements related to the subsequent part-time employment would stem from that employment itself and not the predecessor full-time arrangement.
Some jurisdictions do have language in their ESA about the gap between sequential employments; but I don’t see anything like that in the BC ESA.
However, there’s one more factor to consider, namely, the dynamics and negotiation of the transition from full-time to part-time. Thus, if the employee offered to resign on condition that he/she be hired on a part-time basis, the relationship might be seen as one continuing rather than two distinct employment relationships. In either case, you should probably include clear language to the effect that the part-time arrangement is a separate employment relationship not related to the previous full-time employment relationship and have the employee acknowledge that all claims in regard to the full-time employment have been resolved for good and proper consideration. You’ll need counsel to draft you up something you can use.
Thanks for the interesting Q and I hope we gave you some help–even if it took a while to do so. Glenn