I'm assuming that you are referring to Clitoria ternatea.

1. Seed maturation will depend on local conditions.

2. Daily observation of an individual pod will give you information on the time of shattering i.e. as to when it "throws' its seeds out to reseed itself", note this time data.

3. Use the data to determine the last point before shattering and utilize to collect the individual pods.

3. Optimum harvesting will require frequent observations, note: in practise this means daily inspection - as the pods will not mature simultaneously.

4. Observation is the key!

Yes I mean the ternatea. The double white one. I figured I would have to watch them,but do they rattle when ripe? I mean do the seeds detach from the pod when ripe, before they throw themselves all over the place? Or do they get ripe and still hold on inside till just before they twist and 'blow up'?!

The seeds are attached within the pod (technically referred to as a simple carpel) by attachments known as placentae.
These don't usually break until the pod splits and throws out the seed i.e. the pod dehisces.
It should be O.K. to gather the pods when they are brown and dry.