Perhaps not an upkeep check, as that may tip off the opponent that you have an instant. I think if Sheoldred is on the field, every end of turn should have a hard stop and both players must pass priority for the next turn to begin. This gives time to add a stop on upkeep, but doesn't tip your hand either if you don't happen to have any instants.
Perhaps not an upkeep check, as that may tip off the opponent that you have an instant. I think if Sheoldred is on the field, every end of turn should have a hard stop and both players must pass priority for the next turn to begin. This gives time to add a stop on upkeep, but doesn't tip your hand either if you don't happen to have any instants.