In all previous ascensions, only the physical body disappeared. Clothing and other items were left behind.
Teyla and Dr. McKay's discussion places the time dilation at 250:1. Later, Dr. Beckett states that he has "a date planned for tomorrow night." To which, Dr. McKay replies "Oh no, so we've only got 12 years in here." If they spent 12 years in the time dilation field, that's over 17 days outside of it. Assuming "tomorrow night" is in 36 hours, if they left the field on their first anniversary of entering it, Carson wouldn't even have an hour to get back in time for the date.
After establishing the time dilation at 250:1, McKay says that an hour inside the field would equate to months outside. Assuming a 24-hour day, one hour outside the field and 250 hours inside the field would only be 10.4 days, not months.