Well. Depends on your requirements for the safari. You can do a game drive for like 3-4 hours, and still se plenty of animals.
From Kampala there will be around 4 hours by car to Masindi, which is the biggest nearby city to Murchinson Falls. Remember that you can't count on traffic estimations in Uganda, because, yeah, the traffic can be straaaangeee...
When you arrive to Masindi, there will be around 40 minutes by car to the entrance to Murchinson Falls.
From here you have to drive around 2 hours into the park, where you will reach the Nile as it passes through the park. From this spot you normally cross the Nile by ferry (10minutes), and your game drive (Safari) can begin.
You can do a 3-4 hours of game drive, and then return as well as cross the nile. There will be a lodge close to the Nile (Red Chilli?) where you can stay overnight, and leave the park next day.