First, what is bootchart? Bootchart allows you to check the boot sequence and generate a chart showing how long each process ran during the boot process, and how much CPU/IO they used.
Once installed, bootchart runs on every boot. However, you can edit the variable
GRUB_CMDLINE_LINUX_DEFAULT in '/etc/default/grub' to include
bootchart=disable, which stops bootchart from running at all. Don't forget to run
sudo update-grub afterwards to update GRUB's configuration file.
If you want to run it at a later point, edit the GRUB entry at boot (by pressing the 'c' key at the GRUB menu you can edit the highlighted entry), and remove
bootchart=disable from the the 'linux' line. This will enable bootchart once for the following boot.