Maintenance schedule once per two weeks or more

Not by default :) You'll need to use scheduled tasks and run the following script with some parameters. Save it as Set-Maintenance.ps1 to any path you want:

param([int]$Id,[int]$Duration = 1,[string]$Unit = "Hours")

$Server		= "your-prtg-server-url-or-dns"
$User   	= "your-username"
$Hash   	= "your-passhash"
$DateFormat     = "yyyy-MM-dd-HH-mm-ss";
$StartDate 	= (Get-Date).ToString($DateFormat);

switch($Unit){
	"Minutes" 	{ $EndDate = (Get-Date).AddMinutes($Duration).ToString($DateFormat); }
	"Hours"		{ $EndDate = (Get-Date).AddHours($Duration).ToString($DateFormat); }
	"Days" 		{ $EndDate = (Get-Date).AddDays($Duration).ToString($DateFormat); }
	default 	{ $EndDate = (Get-Date).AddHours($Duration).ToString($DateFormat); }
}

Invoke-WebRequest "http://$Server/api/setobjectproperty.htm?id=$Id&name=Inheritscheduledependency&value=0&username=$User&passhash=$Hash" | out-null
Invoke-WebRequest "http://$Server/api/setobjectproperty.htm?id=$Id&name=maintenable&value=1&username=$User&passhash=$Hash" | out-null
Invoke-WebRequest "http://$Server/api/setobjectproperty.htm?id=$Id&name=maintstart&value=$StartDate&username=$User&passhash=$Hash" | out-null
Invoke-WebRequest "http://$Server/api/setobjectproperty.htm?id=$Id&name=maintend&value=$EndDate&username=$User&passhash=$Hash" | out-null

Modify the script with your server details, username and password. Create a new scheduled task that runs on the days or months you need and run it with the following parameters:

-Duration 1 -Unit Hours -Id 1234 Duration The duration as number
Unit Can be minutes,hours or days. It's hours by default.
Id The ID of the sensor, device or group you want to pause