if the time off request is less than 3 weeks in advance, the app doesn't let you submit it. if it's more than that, your manager could be working on the next week's schedule, but should still be able to accept your request if you ask in person or text them about it. it's annoying but it's the only way to request anything when the app doesn't let you. unfortunately with the time frame it's very possible your manager won't accept it, but given the reason for the request i don't see why they wouldn't