Some missions require the player to play a specific amount of time in the server in order to complete it. Though, the amount of time can be huge, even 200 minutes in total. Not everyone has that much of a free time to play and, anyway, it’s annoying to have a missions like this. I would recommend you to reduce the amount of minutes required to complete this mission or ,if you want to, delete them.

Missions 4 and 5 are difficult, so it’s normal. Goal is not to give the biggest rewards easily

3 things:
I agree.
FIRST
Missions are not enaught good tool for make players play more. In server is too less fun funcions for alone player and game is dead for play against other players that much time in day. Your manipulation trick dont work.
SECOND
Some missions are not difficult but imposible to do sometimes. Missions about killing players are imposible for most of the time because like i writed almost no one play. When players are then are difficult. All missions should be posible to do it or like you prefer “difficult” :P