I have heard that you should not use timers and delays because they become inaccurate when the player experiences drops in frame rate. Is this true? If so, does using delta time correct this issue?
? Timers and Delay are more accurate than Tick without Delta Time 
But you can use Tick and Delta-Time to standardize the tick rate if you so desire. But timers will still be more effective and efficient if you are running various things and want to change it’s rate.