To answer your main question, Barsel.............. not very long at all.
In a bungalow such as yours, I would expect from 10 to 20 minutes.
There are two temperature controls on the boiler for you to adjust.
One for hot water, and one for heating.
Heating temp. is usually set at around three-quarters. Perhaps yours has an "ECO" setting. Experience has shown me that such settings are useless for most systems (unless you have a well over-sized boiler.)
ECO usually means that it's set low to save energy.
Often, this just is nowhere near enough.
If your heating setting (on the boiler) is set high enough, then I would suspect a faulty thermistor somewhere in the boiler (cheap little thermostat type of thingy.)
Or... the circulating pump is not operating properly.
If your rads are set high, and your boiler setting is correct, then I think you should have someone take a look.
Barring the usual suspects, there are several things that could cause this.