JESS: He wasn’t sure how long your mom was gonna be gone for.
RORY: Just tonight.
Emily invited Lorelai to spend the weekend with her, then turned up to collect her on Friday morning (rather than Saturday morning, as a weekend would suggest). Rory indicates that they were only spending Friday night at the spa, yet at the end of the episode, Emily and Lorelai are said to be leaving early when they go home on Saturday morning.
Either Rory is psychic, or she is trying to discourage Jess from thinking he can hang around or pester her all weekend. She may be protecting herself from Jess even more carefully than she protected herself from Dean, out of worry that sex might be on the menu as well as macaroni cheese.
Good thinking, because Jess needs only the slightest encouragement to invite himself to dinner, which was his plan all along.