I crossed international boarder (Kenya-Uganda) for the first time last week. It was a very interesting experience.
Our bus left Nairobi at 8:15 pm and arrived at the Busia Boarder post at 2:00 am. The checks of our travel documents took longer that I had expected. We queued for at least 2.5 hours.
There are two counters where you must pass through at the One Stop boarder post: Kenya and Uganda.
On the return journey, I noticed that the custom department is doing a lot of good work by checking all luggage on the bus to ensure everything is in order. This takes more time but I was grateful that we arrived well.