Several attempts later, all I have managed to upload are several cover images before I get the time-out message. I read in another post about force syncing, so thought I'd give that ago... again timed-out. In that post someone mentioned that it doesn't take long (about a minute for 2,000 albums).... One attempt was about 25 minutes, the others have timed-out between five and ten minutes.

Clearly the uploading problems that I had when the service was introduced haven't been completely fixed!