Immigrant wrote "How about flights, that more then 4 hrs?"
Just adding to what spanishfly69 has said... we do a reasonable number of flights where each sector is more than 4 hours long and which are out & back within the same duty period / duty day (though quite what the 4 hours you mention has got to do with anything, I don't know?!).
Based upon the least restrictive local time of duty start, doing 2 sectors, for a 2 pilot operation (wherein the nature of flydubai's operation means that we're always acclimatised, for the purposes of FTL's) flydubai's 'Flight Time Limitations' (FTL) scheme allows for a maximum 'Flight Duty Period' (FDP) of 13:15.
Given that the report time (1 hour) and turn-around time (45 minutes) are pretty much fixed and are included within the FDP, in order for a 2 sector day to to fit within the bounds of the maximum FDP, you're looking at a maximum BlocksOff to BlocksOn time, per sector (assuming still air), of 5:45 ... and the B737-800 is more than capable of flying that kind of sector length, with a full load (189 pax), albeit assuming that it's not PLTOM limited.
E.g. You can report for work at 9 AM, fly 2 sectors, and so long as you set the brakes 'On' by 10:15 PM, it's all legit; and should anything go wrong, on the day, the Commander always has the option to extend the FDP via use of 'Discretion' (subject to the usual caveats).
Putting this all into perspective, in 2 years I've had to fill-in just 2 discretion reports (and each of those was only for just for a couple of minutes worth of Discretion).
Does that help to answer your question?