Driving in Belize
Went to Belize a few weeks ago and had a similar itinerary to other posters -- arrive in late afternoon/early evening and driving to San Ignacio at least partially in the dark. The TLDR version is that it wasn't that bad and if you are used to driving as part of your daily routine, it is definitely doable.
After reading a lot of the warnings about driving at night and murderous speed bumps from locals, I started to look into hiring a driver or staying overnight near the airport. Well, I ended up biting the bullet and making the drive. I did a lot of research, looking at photos of speed bumps and querying multiple resources. Turns out the nervousness probably wasn't warranted. Here are my observations and takeaways:
Nearly every single speed bump was marked with a pedestrian crossing sign or otherwise. In fact, I saw more "false positives" (speed bump sign where there was in fact no speed bump).
Once you're on the George Price Hwy (the main road to San Ignacio), there's not much traffic or speed bumps until you get to populated areas, where the speed bumps are pretty obvious (aforementioned pedestrian crossings, before/after traffic circles).
There's not a lot of light on George Price Hwy, but there's also not a lot of road hazards.
The Waze app will warn you of most speed bumps, I think there was only one or two that it did not give me forewarning.
Driving in San Ignacio was actually scarier than the George Price Hwy, the streets are narrow with cars parked on the side or bordered by car-wrecking ditches, many are one-way, some are very steep, etc. But there's plenty of other cars to follow, so it's not impossible.
There was another couple that left a little bit after us and they were similarly nervous. We saw them later and they made it through without incident.
Side note, our rental car was involved in an accident. We were parked off-street in a driveway overnight and in the morning discovered someone had dented the rear of our vehicle. I had to spend the entire morning of our first full day at the police station filing a report. I did not get Crystal auto insurance and could not reach anyone at my credit card company's insurance provider because it was the weekend, which was a PITA. I would advise getting rental car insurance but not sure how much it would have helped, because I think I heard the Crystal rep tell someone else the deductible was $1200. In a story twist, the person who hit our rental car actually showed up and took responsibility. Final outcome is still TBD.