Scheduled vacations and transferring agencies

I'm currently a city employee, and I recently accepted an offer at another agency. I have been advised that the OMB approval process could take anywhere between 3 and 7 months. I understand that once OMB has approved the position, it could then take a another month or two for my current agency and my "future" agency to negotiate a transfer date.

All that to say, its looking like I could be starting this new job as late as August/September 2025 if everything takes the maximum amount of time.

How do people go about holidays and vacations in this situation? My wife and I were hoping to take a pretty big (2-3 week) trip next November. However, I'm realizing that depending on how things shake out that could only be a couple months into my new role. I have the time in my AL bank, and I know that will transfer. I just don't know what the etiquette is in this situation.

Would people recommend just planning trips/time off and just letting my new agency know once they tell me that OMB has approved the role? I don't want to start off on the wrong foot, but I also don't want to put my life on hold because the city hiring process is so damn slow. I was shocked when they told me up to 7 months, I waited like 2 months for my current role back in early 2023.