How much time do you think, it takes to fire a interceptor missile?
Swordfish LRTR(developed with Israel) has a range of 800Kms i.e even if placed 200km within Indian territory, It can monitor almost entire Pakistani airspace.
In Worst case scenario even if it takes one minute for the radar to acquire target resolution(typically a radar can start tracking a target with in few seconds of being plotted)
Interceptors still have 3-4 minutes to fire, before the missile reaches its target(New Delhi)
These are solid fueled interceptors, are always ready to fire on press of a button..All they need is a target resolution.