"As 3nm is the minimum radar separation "
I think Heathrow ATC is allowed until 2,5 NM on the last 10 NM leg
ICAO allows 2 NM if a local safety case demonstrate the feasibility (Need of high speed exit taxiways, radar integrity etc..)
"As the headwind increases the time interval between traffic spaced 3nm apart .."
For the annualy few days of real strong headwind, just ask the crews to keep higher indicated airspeed than as long as theA/C can do it and the difference is peanuts...The difficulty is more on the radar vectoring side when, with high wind gradients ( in force and direction) the accuracy of the sequencing from downwind to ILS interception is decreased
"in order to preserve an acceptable time interval (time based spacing.."
The last EUROCONTROL real time simulation have not proven the efficiency of the so called "time based separation"