Edit: I just realized this is not what you asked, but it's an arguable thing. Some would say to let the server or admins control when the game changes maps, but at the same time, if the server has no time limits or there are no admins on, the map will play forever. If you need help, I've provided a quick tutorial below.
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Ok, I'm gonna be a bit quick, but the entities and things I'm going to explain to you should work. I have tinkered around in some of these areas before.

If you are wanting to create a set number of rounds, you are going to need to create a math_counter entity and a game_end entity. Set your Math_counter's fields as follows

--Math_Counter
name: [can be anything really]
start disabled: no
initial value: [the number of rounds you want the players to play]
Minimum Legal Value: 0
Maximum Legal Value: [Max number of rounds you want the player to be able to play. Should be the same as initial value]

Set the out out to:
Output: "onhitmin"
Target entities: [the name of your game_end entity]
Via this input: EndGame
After a delay of second: 4 (note: let the player see the MVP's before the scoreboard by making this at least 4 seconds)

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How to use this setup:

I will describe this using the game_round_win entity; however, you should be able to apply this to Flag and CP_master entities as well.

on output:
Output: OnRoundWin
Target entities: [math_counter name]
Via this input: Subtract
parameter Overide: 1

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Post me if you have any problems.