I have 4 mos old twins who still very much call the shots for when to eat/ sleep, when did you start a schedule?
First natural BFP June 2013
Ectopic July 2012 with fallopian tube and ovary removal 
First IVF (after 1 cancelled cycle) Jan 2014,
ER 1/16
ET 1/21
Beta 1/31 BFP!
Beta 2: 400
Beta 3: 700
Beta 4: 11,000
Beta 5: 45,000
1st US 2/18: TWINS!!! 
EDD: 10/10/14
Delivered via c section 9/17/14, B/G twins
Re: When to try schedule for twins?
Around 6 months is when I started being cognizant of a schedule. They don't stick to it every day (right now my boy is napping and my girl is being VERY stubborn, grrrrr), but there is a general schedule that they follow.
Baby Boy #1 born 1/15/2010
Babies #2 & #3 arriving Spring 2014 (EDD June 18)