A little detail here. I have said it before on this forum, that one of the tactics that jets use to attain more speed to avoid interception, is that they drop their payload, in one of my argument on PDF before.
It is quite possible that these aircrafts had targets but upon seeing an interception incoming, they dropped their payload to attain full speed and get out.
As for response time. The Mirages have a top speed of 2300 km/h, they can cover the distance to Balakot in the time of less than 5 minutes.
This is just a possible explanation on the sequence of events. I would hold my comments on it till details are more clearer, although the photos released by ISPR support the above narrative.