The interesting part is that he actually denies being abducted. However that may be due to the fact that the military would not allow him to undergo regressive hypnosis and he was probably too scared of being declared mentally unfit for duty if he did claim that he was abducted by a flying saucer. It's also possible that the aliens used the power of suggestion to make him keep quiet about the incident in the same way they make abductees "forget" their experiences. Another possibility is that he is simply worried about the ridicule he would receive if he were to go public about his account of alien abduction.
I have read a few online comments about the watch in question and some say based on photos of Valdes that it is probably a Seiko LC Quartz Chronograph model with a time and calender display. These watches came out in the mid 1970s so it would be consistant with the time.
As far as I know it is possible to travel to the future because time slows down as you approach the speed of light but I don't know how it could work in reverse that would see you age 5 days when you have only been missing for 15 minutes. Perhaps it has something to do with travel through wormholes across different dimensions or something