Booting has distinct stages: firmware checks the hardware, the operating system loads its core, drivers initialise, then your account signs in and starts its programs. A delay lives in exactly one of those stages.
Firmware delays feel like a long blank screen before any logo. They usually mean the machine is waiting on a device, such as a slow drive or a network boot attempt that has to time out.
Delays after the logo are the operating system loading drivers and services. This is where an old mechanical drive hurts most, because thousands of small reads happen in sequence.
The final stage is the one you can control. Everything set to launch at sign-in competes for disk and processor at the same moment, which is why the desktop appears but stays unusable for a minute.