Mostar usually works better when it gets one night
Mostar can be done quickly, and that is exactly why a lot of travelers undersell it. The city is compact, the bridge area is obvious, and on paper it can look like a short scenic stop rather than a real overnight. In practice, Mostar often improves once the middle of the day passes and the place gets quieter.
Who gets the most from staying?
Couples, photographers, slower travelers, and anyone building a Bosnia-focused route usually get more value from an overnight than from a rushed stop. The evening and early morning mood is a big part of what makes Mostar work. If you miss that, you often get the busiest version of the city rather than the best one.
When a day trip is enough
If the route is already overloaded and the goal is simply to see the bridge, walk the old town, and keep moving, a day trip can still be fine. Mostar is small enough that you can understand the core quickly. The downside is that it can feel more like a transit memory than a place you actually stayed in.
Why the timing matters
Mostar changes with the light and with the crowd level. A calmer dinner window or an early walk near the bridge can shift the whole mood of the stop. That is usually what pushes the city from photogenic into memorable.
The honest answer
If your route can handle the night, Mostar is usually worth it. Not because it is huge, but because it feels much better once you let it slow down.