If you control more than one Grave Pact and a creature you control dies, each of the triggered abilities will trigger

Synergy, Griefing, Staples, Building a Doran Deck ) Commander Starter Kits 1 (kick start your allied two-color decks for $25) Commander Starter Kits 2 (kick start your enemy two-color decks for $25) Commander Starter Kits 3 (kick start your shard three-color decks for $25) Commander write-ups Ive done (and links to decklists) : Zurgo Bellstriker (Bellstriking Like a Boss) Dragonlord Ojutai (Troll Shroud) Karrthus, Tyrant of Jund (Dragons, Megamorphs, and Dragons) Dromoka, the Eternal (One Flying Bolster Basket) Shu Yun, the Silent Tempest (Tempests and Teapots) Tasigur, the Golden Fang (Hatching Evil Sultai Plots) Scion of the Ur-Dragon (Dragon Triggers for Everyone) Nahiri, The Lithomancer (Lithomancing for Fun and Profit) Titania, Protector of Argoth (Titanias Land and Elemental Exchange) Reaper King (All About VILLAINOUS WEALTH) Feldon of the Third Path (She Will Come Back to Me) Sidisi, Brood Tyrant (Calling Up Ghouls with Sidisi) Zurgo Helmsmasher (Two Times the Smashing) Anafenza, the Foremost (Anafenza and Your Restless Dead) Narset, Enlightened Master (The New Voltron Overlord) Surrak Dragonclaw (The Art of Punching Bears) Avacyn, Guardian Angel

Of course, if the first card in play explicitly causes it to become day or night it simply becomes day or night
That said, we dont have EDHREC data because no one has built yet but, and I dont think Im out of line saying this, as someone who has written a column about building EDH decks for 8 years, I think I understand how the format works to an extent and Id be delighted to make some predictions based on the cards and how they work