When a card or an effect is activated during this timing, it is considered to be activated in response to both the Monster's Summon and the preceding Chain Link. For an Inherent Summon, this timing is after the Summon negation window. For a Summon by card Effect, this occurs immediately after the monster(s) are Summoned. Cards like "Solemn Warning", "Solemn Judgment", etc. that negate the Summon of a monster cannot be activated during this timing; they can only be activated in the Summon negation window. Summon Response Window would miss its timing if the Summon is not the very last thing in the chain.