Are they able to deliver bags with a delay of two - four days? We are planning to keep a larger bag with us which we share and send one on to certain hotels with additional clothes etc as we are there for 3 weeks.

I've had hotel clerks ask me when I want the bags to arrive, so I think that within reason, a delay of a couple of days should be possible.

Incidentally, I highly recommend printing out the Access pages of the Japanese websites of the hotels you will be staying it. This is useful not only for forwarding bags but also for showing to cab drivers (since the map on the Access page will show how to reach the hotel from the nearest major transit station or landmarks) or even to pedestrians, if you choose to walk from the train or subway station and find yourself in a maze of narrow streets.

I once got lost trying to find a small ryokan in Nagoya, and the local people in the subway station area didn't know it by name, but as soon as I pulled out the map, they realized that it was across the street from a temple that they knew. They gave me directions to the temple, and I was able to take it from there.