She didn't plan on lingering around for as long as she did at Travis's house. She did expect to arrive later than the time frame she told Burns, but not that late. I believe she planned on telling the "I got lost" story from the get go. It's part of her coverup. We know that she planned on turning off the cell phone for at least 10 hours (the time it would take to get in and out of Arizona as quickly as possible). She knew this cell phone issue would look incriminating. If she had told Burns that she'd be arriving at 2PM instead, she'd eventually have to account for the missing 10 hours. Detectives would have noted that this cell phone time gap gives her enough time to ghost her way in and out of Mesa for the murder. To help get around it, she tells Burns that she'll be arriving at 9:00AM -- this gives impression that she is 1) innocent of premeditation and 2) that her original cover story of getting lost in Nevada is true (hence the reason she couldn't find her cell charger or buy a new one to charge her battery). Basically, the "I got lost" story was concocted to explain the cell phone, and telling Burns of an earlier arrival helps to corroborate that as her DELAY is proof that she got LOST. Get it?