SHARES has problems with direct flights. Seat assignments is one of them.
PMUA used to do a nice job with them -- you could select seats for the different legs online.
Pretty much anytime you think you'll have a quick call with UA, assume it'll take half an hour. It's not an unreasonable estimate. Most calls are 20-30 minutes, and I've used a tremendous amount of staff time on basic items since 3/3.