C-19. No carrier regardless if federal or private is committing to overnight deliveries as medical and other supplies have priorities. This does not give a pass for things to get lost but everyone should assume there is pressure in the logistical space.
If the hobbyist is paying for shipping then the onus is on the hobbyist to put the correct amount on it. This isn't difficult to figure out if you have a scale at home. Weight the package, look up shipping rate and package size, apply the correct number of stamps. If you are still unsure grab your personal PPE, get on transportation of your choice, and head to the local post office. Stand in line, ask how much postage is needed, pay for it, apply, and off you go.
Another choice is to use a ICP vendor who includes the shipping label and cost for you.