I post this here for the people who doesn't know what is happening at the end phase of the turn that a spirit monster was normal or flip summon and has its effect negated by the effect veiler
Both effects occur at an unspecific point in the End Phase. The turn player has the chance to activate effects or resolve lingering effects. He or she may pass priority to the opponent to do the same. The opponent may pass back, and at this point the turn player must activate mandatory effects or resolve mandatory lingering conditions.
So.. Ideally, the turn player will want to take that first opportunity to activate the effect of their Spirit Monster, so that it is still negated and it remains on the field.
Both effects occur at an unspecific point in the End Phase. The turn player has the chance to activate effects or resolve lingering effects. He or she may pass priority to the opponent to do the same. The opponent may pass back, and at this point the turn player must activate mandatory effects or resolve mandatory lingering conditions.
So.. Ideally, the turn player will want to take that first opportunity to activate the effect of their Spirit Monster, so that it is still negated and it remains on the field.