depends what you call convenient
1.our national site 9292ov.nl list ALL connections-bus, train, ferry-you name it they have it
2.most people only think of train: walk to nearby small station-take ANY train south toward Amsterdam- change at SLOTERDIJK-both ways have 4-6 trains/hr all day, total time maybe 25-30 mins.
3.by BUS=can be much cheaper,after9.00_lvs direct from in front of Schans-to A'dam CS=-and then train, also 2/4 per hour. all day-hardly needing to worry about times etc.
ZS is a tiny museum -old style ''enclave'' with a big museum next to it. there is AFAIK NO accomm at all there-but probably nearby, does that really warrant a change of HTL for 25 mins?
My best advice would be: go to Am-CS morning-store luggage (assuming you dont want to carry it all day, nah?)-take bus to ZS-from big busstation to far LEFT of CS-when coming ut, a green Connexxion bus-look around-most people do that in 25 mins [but those are chinese)-take bus back-retrieve luggage-buy train ticket to Haarlem-run to catch train-as you dont note the next one is in 6-8 mins!