When a linesman calls a penalty, must he/she wait until a stoppage of play
to call it?

Last night during the Beanpot Final, BU goaltender Fields got a slashing
penalty while BU carried the puck up ice for two great scoring chances.  The
Linesman waited until the NU goaltender secured the puck for a stoppage in
play to call the penalty way after BU pounded chances on the NU net.

Should he whistle the play dead with the offending teams' possession similar
to a delayed penalty call?  Also, if BU scored, would they wipe out the goal
with the Fields penalty?

Worried that I lost my mind with my hair and my humble apologies if I
overlooked a rule somewhere.  Thanks for the guidance.

'til then. Carpe Diem.

Make it a Great Day.

--John.