Mosquitos are a daily thing here in Indonesia. They appear usually between 7-8.30am then again between 5-6.30pm generally, but depending where you are it can be anytime. Here they tend to hang around moisture so any plants that have been watered etc etc. I do my best not to get bit, but average about one a week as I am very careful.
As mentioned some can carry and spread virus. When I was in Indonesia the last time, a friend of mine got bit and finished up in hospital for 3-4 days. The bite swelled up and he became drowsy. It turned out it was the bite from the mossy.
We have a lotion we can put on here which I use if I'm going to places where the possibility of mosquitoes is increased, it's called Soffell. If you ever come across it, I recommend it.