Here's a guide – ATOP for Linux server performance analysis (Guide)
A handy shortcut for reading previous days, you can dive into yesterday's log with atop -r y and the day before with atop -r yy and so on. Once you're in then t and T skip forwards and backwards in 10 minute steps, and you can use other keys to flip between different screens like CPU, disk, memory, etc, see the guide. This should reveal what was maxing out the CPU during each period.