In short — you don’t need to worry about that. The cronjobs will be executed in by the time you set, regardless of the line so to speak.
The cronjob looks fine in general, but you might want to add logging to it it by adding
2>&1 >> /home/pi/hdmi_power.log or similar.
Alternatively, you might want to look into Timers in systemd. They’re a bit more complicated to set up, but do provide you with logging and other goodies.