I just looked at the Katiba again after reading Ghai's comments. Assuming OKOA Kenya submits their petition today to the IEBC, the earliest a vote can take place would be July 2015.
If they go ahead with their slow timetable, the earliest one would vote is March 2016.
1. IEBC needs 3 months to verify the signatures
2. MCAs need threes months to eat bribes and eventually vote their prejudices
3. In event MCA pass it, it then goes to parliament. The time to be taken is not specified but the constitution grants the bill priority over other bills by recommending action without delay. That in my book reads like 14 - 60 days
4. Campaigns take 3 months