My server Lamia has been pretty good about it. The sad part is that the parties operate during the NA morning hours and by the time I get off of work, the three scouring parties have eliminated every S and A rank out there.
They seriously need to make S and A ranks spawn more often for the ppl who play in the afternoons. But, if you happen to be off that day from work, are in one of those parties, and make it to the nm within a reasonable amoutn of time after it is spawned, you might be able to get in 1 hit in the 4 seconds before it dies. Just make sure that you are in a party so you can get the maximum credit.
For the record:
S rank - spawns 1 per week (need large party)
A rank - spawns 1 per day (need small party)
B rank - spawns 1 per hour (soloable)
The weekly hunt is B rank, spawns 1 per hour, and is soloable.