As crew, we can move around the aircraft "when safely established in the climb and clear of low level turbulence", that normally will occur quite quickly after take off. Your seat needs to be in the locked position during take off so it can protect you and take the strain in the the event of a rejected take off etc. Once in the air this no longer applies, so I see no reason why you can't convert it into a bed and get to sleep ASAP. Now can you lower the foot stool without undoing your seatbelt?