When do the legendary portals open in ORAS?

Question

I know, dumb question. But I'm curious

Comments

After getting the national Pokedex, maybe?

Answer 1

In order to reach all but 2 of the Rings, you must be able to Soar using the Eon Flute. Steven does not give the Eon Flute to you until Team Aqua/Magma releases Kyogre/Groudon (respectively) from the seafloor cavern. At this point, you would have access to all the Mirage Spot Ring Encounters, provided you meet their other requirements. You do not have to capture/defeat Kyogre/Groudon to access these events. However, if you are leveled on par with the game content to this point, you will be fighting uphill, as Kyogre/Groudon are at level 45, while all Legendary Encounters are at level 50.

Heatran is a bit of an exception to this. In order to reach the Ring in the depths of the Scorched Slab, you must first complete the Kyogre/Groudon encounter beneath Sootopolis. You will encounter Gym Leader Flannery, who mentions looking for a very rare Pokemon in the area, but that she was unsuccessful.

Finally, while you can reach the Sea Mauville any time after you have received the HM and Gym Badge for Surf, you will not be able to being the side-quest associated with Ho-oh/Lugia until after the Kyogre/Groudon encounter beneath Sootopolis. The result of the side-quest will be the Clear Bell for Ho-oh in Omega Ruby, or the Tide Bell for Lugia in Alpha Sapphire. After obtaining your version's Bell, you can return to the Sea Mauville, locate your version's Ring, and begin your Encounter with Ho-oh/Lugia.

Answer 2

You are able to access all Legendary Pokémon and their portals after you defeat or capture Primal Groudon/Kyogre.

Source: Experience

Answer 3

To elaborate on the prior answers,

Each Portal has its own respective legendary Pokémon habiting it.
Mesprit, Uxie and Azelf share one however as do Raiku, Entei and Suicine. These Pokémon are found at different times in the day and on different days of the week.
(As I understand it too, to be able to access the three legendary dogs as mentioned above you need to have caught and own both Ho-oH and Lugia)

Some of the harder legendaries to catch, Giratina/Landarous/Kyurem (there may be a few more) require particular Pokémon to be in your party to be accessed.
For Example
Giratina needs Palkia and Dialga
Kyurem needs Reshiram and Zekrom
Landarous needs Tornadous and Thunderous etc.

Obviously this does mean some trading to do unless you own the other series part but if your not so lucky you can always gamble on GTS or ask your friends.

I'm afraid I don't have any sources to link to as this is all from learned experience but I can guarantee there are pages out there which describe exactly how and when the portals appear

Comments

To get Entei, Suicune, and Raikou, you do not need to own both Lugia and Ho-oh, you just need to have either one in your party to be able to catch them.