My understanding is that you are trying to use the 'timer' function to execute a script (that plots a figure) every 300 seconds.
In order to do that, you can use the following code as a reference and implement it for your use case:
t = timer; % create a timer object
t.Period = 300; % set the period
t.TasksToExecute = 3; % Number of times the timer callback function has to be executed
t.ExecutionMode = 'fixedRate';
t.TimerFcn = @(~, ~)figure;plot(1); % I have specified a basic figure plotting function. This can be changed as per your use case.
start(t);
