Nice idea.....But contrary to everybody is saying it wouldn't increase the time of the technique but the range....For example, Kakashi can use Kamui at long distance as observed against Pain, Deidara, Gedo Mazo, ect...On the other hand, Obito can use his Kamui at close range and on himself making him intangible for 5 mins....If Obito had both eyes then he wouldn't have to touch his victims to suck them in...Instead, he could just suck them in at long distances or opt to teleport himself and suck them in and if they escape them he would suck them in anyways.....That's what I think since we have seen that each eye always has a different power as seen in Sasuke's, Itachi's and Obito and Kakashi

...However, It might be possible too to increase the time, since Madara said himself that to awake the true power he need both eyes, which means that Obito isn't at his 100% and yet he is raping a lot of people lol