Delivery times are up because of the volume of business. As essentials business falls down (or 'if', if people get used to using Amazon over their local store), delivery times will fall as well. This isn't a meaningful long-term criticism.
My take is that they are experiencing something akin to holiday season levels of sales, but that they're not staffed for that kind of volume, since it's spring. So they temporarily shut down inbound shipments of non-essentials so that they could free up warehouse staff for outbound shipments in general. If this is correct, then I think their delivery times are dependent on two things: 1. how quickly they can staff up for the increased volume, and/or 2. how quickly and to what degree retail spending shifts back to physical stores. But demand for essentials returning to normal will probably not make a difference.