Obstruction calling method

[rafking]

NFHS - I am looking for the proper method for calling obstruction at home when other runners are still active.

2 outs. R3, R2. Batter hits grounder to F6. Throw comes home and catcher obstructs R3. You have a delayed dead ball. Do you immediately yell 'safe - obstruction' so the catcher knows to go try and throw out the runners still on base?

I can see the catcher starting to pout then coaches come out to argue; when do you call time? I do not want to punish the runners at this point.