I used this to fix this problem

TimeRangeSelectedJavaScript="FixWidth();" VisibleRangeChangedJavaScript="FixWidth();"

function FixWidth(){
document.getElementById('ctl00_ContentPlaceHolder1_DayPilotScheduler1').childNodes[1].childNodes[0].childNodes[0].style.width = '100%';
}
$(document).ready(function(){
document.getElementById('ctl00_ContentPlaceHolder1_DayPilotScheduler1').childNodes[1].childNodes[0].childNodes[0].style.width = '100%';
});

Sp