It doesn't seem like Obito has much a future left, so let's get cracking.
Tobi uses Izanagi against Konan (Page 10)
Tobi's Izanagi lasted for 10 minutes (Page 3)
Tobi was definitely referring to himself using the complete form of Izanagi. Recall that Danzou had 10 eyes and each eye had a 1 minute duration of Izanagi. Tobi is able to use at least 10 minutes worth for an eye sacrifice.
We also know that with each eye Danzou used, his chakra dropped significantly according to Karin. His huge chakra loss is due to the fact that he is not an Uchiha. While this was not specifically stated in chapters 510 or 479, we know that a non-Uchiha using Sharingan consumes a lot of chakra (ie Kakashi).
Now Tobi stated that Danzou didn't have full control over Hashirama's powers (Page 12), so this is why his Izanagi had a time restriction (of 1 minute). Tobi goes on to explain how Orochimaru realized this as well, thus implanting 10 eyes to lengthen the duration of Izanagi for Danzou.
The complete form of Izanagi requires full control over both the Uchiha DNA (Sharingan) and the Senju DNA (Hashirama cells). With this, one can use Izanagi without a timelimit per se, but rather a chakra limit. Tobi needs to use chakra to use Izanagi, so the duration of the doujutsu is directly proportional to the amount of chakra that he uses. Once Tobi runs out of chakra, he can no longer use Izanagi.