For this an easy way maybe to use capacitors. So with an RC circuit you can control when to activate a transitor acting as a switch, to let the signal go out. But then you will have to calculate the R and C for the times you want, and also the values (voltage and current) to saturate the transistor. Or in other case can use OpAmp instead of the transitor and do a voltage comparator, so when the voltage in the capacitor goes up to the votage in an voltage divider, in the other input, the the output will be activated. Again the times you will have to calculate the values of RC to set the charge and discharge time.