The best use of Sundial is to “break” cards that have abilities that trigger at the beginning of the next end step or at the beginning of your next end step abilities that you'd like to avoid. Since we're talking about Commander here I'll go ahead and point out that you want Sundial of the Infinite in your Sedris the Traitor deck since it works so sweet with his ability. The unearth ability can only be played as a sorcery brings the creature back from the graveyard gives it haste and says “Exile it at the beginning of the next end step or if it would leave the battlefield” (this is the current Oracle wording which is a bit different from the printed reminder text).
The key thing to look for is that word next. Say you've got Sedris in play and you want to bring Nekrataal back from your graveyard with unearth. Bring him back go ahead and attack with him and if he survives go to your end step (the next end step). Put the exile trigger on the stack then go ahead and activate Sundial to sweep that trigger right off the stack and keep your Nekrataal around indefinitely (though keep in mind that if he leaves play it will still trigger that other exile effect so his additional borrowed time is still borrowed).
this is 100% true info?
The key thing to look for is that word next. Say you've got Sedris in play and you want to bring Nekrataal back from your graveyard with unearth. Bring him back go ahead and attack with him and if he survives go to your end step (the next end step). Put the exile trigger on the stack then go ahead and activate Sundial to sweep that trigger right off the stack and keep your Nekrataal around indefinitely (though keep in mind that if he leaves play it will still trigger that other exile effect so his additional borrowed time is still borrowed).
this is 100% true info?
Remember the effect must say "at the beginning of (the next/your next) end step". Sundial doesn't work that way with "until end of turn" effects.