When it is actually comfortable to be outside?
I built an ERA5-Land pipeline computing temperature across coastal and inland Montenegro, to find the hours and the places where being outdoors is comfortable (no more than 25-26C as set by the client).
First check: diurnal temperature cycle
Temperature by local hour for popular (near-)coastal locations (July–August, 2001–2025 average). Grey is before sunrise/after-sunset time.
We see that comfortable temperature window is potentially only in the morning, not in the evening.
Now let's look at apparent (feels-like) temperature under the sun for selected locations -->
Feels-like under-the-sun temperature in Budva
I checked safe temperature window week-by-week. Budva is safe only before 7 am, end of August is better than July and mid-August.
Feels-like under-the-sun temperature in Kolasin
Let's compare temperature comfort in the mountain location: Kolasin (954 m asl) — it is safe before 10-11 am and in the evening, from 17-18 pm!
Advised solution
I recommended avoiding staying at a coastal location at all. If opportunity to swim at sea is really important during the trip, I recommended to split the trip between a coastal an a mountain location.