How to perform certain actions for a specific amount of time in a loop

I have this function that seems to do what you want, It is written in Javascript but rewriting to VB should not be a problem.

function DoStuff(delayMS)
{
let start = Date.now();
  
  while(Date.now() - start < delayMS)
  {
    if (Aliases.Stuff.Exists)
    {
      Delay(500);
      Aliases.Stuff.Close(1000);
      return;
    }
    Delay(100); //Short break before checking again
  }

Log.Warning("Stuff did not exist!");
}

The function checks if something exists and closes it, It waits for a max of {delayMS} miliseconds 

If it doesn't exists within the given time it posts a warning to the logs

Doing something have x amount of time that can not be calculated. This JavaScript code would be more realistic to expectations.

function TimeIt()
{
  Now = new Date().getTime();
  ExitAt = Now + 600000; // add 10 minutes in milleseconds
  while (Now < ExitAt) {
    // Do something
    Now = new Date().getTime();
  }
}