You might get lucky and be able to use the WB straight over the OB stain, if you let the stain dry/cure for a couple weeks, but I'd use the shellac anyway. Zinnzer Sealcoat® works great for that.
I'm in the same dilemma. I checked with General Finishes and they said let the stain cure for a minimum of 72 hours. I'm going to give it 6 days because I can't get to it till this weekend.