The effect to Synchro Summon during your opponent’s Main Phase is a Quick Effect.
You cannot activate the effect to Synchro Summon multiple times in the same Chain.
You can activate the effect to Synchro Summon during your opponent’s Main Phase 1 or 2. Using it when your opponent wants to end Main Phase 1 does not force them to continue into their Battle Phase.
You send the Synchro Material Monsters to the Graveyard when you resolve the effect to Synchro Summon.[Notes 1]
You must Synchro Summon when the effect resolves, if possible, using Formula Synchron and the faceup monsters are [sic] available to you. If you cannot, your opponent can verify that you have no monsters in your Extra Deck that can be Summoned.[Notes 1]
Judge Program Forum Rulings
These Ruling(s) have not been confirmed as applicable to the TCG.[Notes 2]
↑ 1.01.1The Synchro Summon occurs immediately after the effect resolves, not when it resolves.
↑Konami Judge Program Rulings are considered unverified, as their source(s) are not publicly viewable. They are not confirmed as applicable to the TCG until they have been officially published by Konami.