They do support scheduled shipments for a few customers who pay significant premium for that. What they cannot reasonably do is to do internal buffer for their own internal shipping capacity because the whole system simply is not designed for that. There is some somewhat significant and usually unnecessarily large capacity (because it is optimized for through-put, not storage efficieny) for warehousing of in-transit packages, but the current demand is so large that warehousing capacity is the limiting factor.