Add 15 minutes time steps (#5613)
Add 15 minutes time steps (#5613)


jtcorbett/Chart.js,simonbrunel/Chart.js,touletan/Chart.js,touletan/Chart.js,touletan/Chart.js,chartjs/Chart.js,chartjs/Chart.js,touletan/Chart.js,nnnick/Chart.js,chartjs/Chart.js,simonbrunel/Chart.js,jtcorbett/Chart.js,chartjs/Chart.js