I went on a 3 mile walk the afternoon of my transfer and everyday during my two week wait. I had tons of nervous energy so couldn't sit still. I have my baby from that cycle.
My RE's office does not recommend bed rest. I didn't need to fly anywhere but was told they have women go straight to the airport after transfer and get pregnant. I honesly think moving around may be good for the blood flow so 18 hours sounds like plenty of bed rest to me. Stay away from hot tubs and saunas as you don't want to overheat.