Unsure of how to use a switch that is time dependent
You have not provided your programming language of choice, so I'll answer in pseudocode which can then be adapted to the specific environment.

It should be possible with the following construction:

do {
  if (on_line) {                 // this may be a variable you update periodically or a method to call every time
    last_time_line_seen = now()  // remember that we have seen the line at this time
    follow_line_as_usual()
  else {                         // if the line is currently lost
    if (now() - last_time_line_seen &gt; 2_SECONDS) {
      turn_around_go_forward_catch_line()
    } else {                     // we are off the line but the two seconds have not passed yet
      do_something_else_like_go_forward()
    }
  }
  wait_some_time()               // optional, may not be needed
} while(stop_condition)          // if you have a stop condition


This works by storing the timestamp of the last known time when the line was seen, and checking if that was more than 2 seconds ago in the case the line is currently lost.

I haven't seen in your question what your robot should do if it has lost the line but the two seconds have not passed yet so feel free to fill that part with any behaviour.