The time to have reported it was when it happened. But you know now for the future. The reason for doing it immediately is that ATC will be looking out for it and possibly building up a picture for the Police helicopter who when launched in the right direction, appear to be rather effective at catching the perpetrators.
To date we have been lucky in so much that there has been no (log term) injuries or deaths as a result of l@sers. However, if the miscreants who insist on doing this carry on it will only be a matter of time before we have a really unpleasant outcome. Generally, in the UK the courts give a custodial sentence to those found guilty of endangering flights but rather amazingly, it's considered a 'minor' offence in others.
PM