When Etali's ability resolves, you can cast any number of the exiled cards only right after you exile them (C.R. 608.2f), and not later; casting those cards is a one-shot effect (C.R. 610.1; compare the second ability of Chandra, Pyromaster with her third ability).
Is this like Spell Queller when leaving the game on any time?
I mean, like if it's a creature the exiled card, I can also cast it when this attacks? I'm sure I could, otherwise would say it, right?
Spell Queller is no different from Etali in that respect: the exiled card can be cast only when Spell Queller's last ability resolves, and not later (C.R. 608.2f). If a player were allowed to play or cast the exiled card at some other time, then, for example, text like "this turn" or "for as long as that card remains exiled" (examples are Ornate Kanzashi and Gonti, Lord of Luxury), or a separate ability (an example is Nightveil Specter), would be used. Either approach would result in a continuous effect (under C.R. 611.1a or 611.3b, respectively) allowing the exiled card to be played or cast.
It's worth noting...
Two kinds of effects are being discussed here: they are similar in that they allow you to play cards from exile (while normally cards can only be played from your hand); they are different in that only one of them allows you to disregard 'sorcery-timing' restrictions.
1- Effect allowing you to play cards 'now or never': Etali, Primal Storm & Spell Queller.
This kind of effect allows you to play the cards immediately, regardless of 'sorcery-timing' restrictions.
Creature spells, for example, could be played right in the middle of combat.
2- Effect allowing you to play cards 'until some specific condition is met': Chandra, Pyromaster, Gonti, Lord of Luxury, Ornate Kanzashi, Nightveil Specter.
This kind of effect does NOT allow you to break timing restrictions: non-instant spells may only be played if 'sorcery-timing' restrictions are met.
BChainer, Dementia Master(Big Mana/Reanimator)
BRRakdos, The Showstopper (Mass Life Loss/Ramp)
BUThe Scarab God (Zombie Tribal/Control)
BWKarlov of the Ghost Council (Life Gain)
BGJarad, Golgari Lich Lord (Stompy/Dredge)
BRGProssh, Skyraider of Kher (Tokens/Non-infinite Combo)
BChainer, Dementia Master(Big Mana/Reanimator)
BRRakdos, The Showstopper (Mass Life Loss/Ramp)
BUThe Scarab God (Zombie Tribal/Control)
BWKarlov of the Ghost Council (Life Gain)
BGJarad, Golgari Lich Lord (Stompy/Dredge)
BRGProssh, Skyraider of Kher (Tokens/Non-infinite Combo)
I mean, like if it's a creature the exiled card, I can also cast it when this attacks? I'm sure I could, otherwise would say it, right?
Two kinds of effects are being discussed here: they are similar in that they allow you to play cards from exile (while normally cards can only be played from your hand); they are different in that only one of them allows you to disregard 'sorcery-timing' restrictions.
1- Effect allowing you to play cards 'now or never': Etali, Primal Storm & Spell Queller.
This kind of effect allows you to play the cards immediately, regardless of 'sorcery-timing' restrictions.
Creature spells, for example, could be played right in the middle of combat.
2- Effect allowing you to play cards 'until some specific condition is met': Chandra, Pyromaster, Gonti, Lord of Luxury, Ornate Kanzashi, Nightveil Specter.
This kind of effect does NOT allow you to break timing restrictions: non-instant spells may only be played if 'sorcery-timing' restrictions are met.
RULES OF MAGIC :
http://magic.wizards.com/en/game-info/gameplay/rules-and-formats/rules