If you reach out to a coach before mid-January you will hurt your kid's chances.
Above mite Major there are few if any walk-ons for the Top teams in the EHF. Not sure how the T1 teams work but most (if not all) of the rosters are full well before tryouts at the Elite level.
You have to wait until the season is over, although most teams break this rule. Come February, kids are always “sick” for practice