Atom — the hackable text editor, is a tool which can be customized to do anything in an editor.
It is an open source desktop application built on latest web technologies and it runs on Electron[a framework for building cross platform apps using web technologies] which uses Chromium, a battery hogger & node.js.
Atom comes with a built in package called Timecop. This package helps in identifying the time consuming packages which eat the startup time. This timecop package helps in making the editor faster.
Click on Packages > Timecop
timecop reports the time taken by each package/theme. If a package takes more than 25ms to load, it is considered to be a slow performing package.