Akar got a reaction from Mark Ingram in DoF Blur Filter Unusable 188.8.131.52
It highly depends on the resolution. I checked it roughly in function of Mpx and the results are as follows:
for 2 Mpx about 1 sec,
for 14 Mpx about 20 sec,
for 16 Mpx about 110 sec.
This is not the linear function. For 24 Mpx f.e. it may take a long long time.
I used this function several times in latest betas, but always for 2 Mpix, so I didn't notice any problem.