That is incorrect. Bambu Printers can use M400 as a general wait time.
Example from the Bambu Specific G-code Thread
M400 Pause - Can be used 2 ways*
*Pause Method 1 Example/Description:
Including S# with the M400 command pauses for # seconds
M400 S30
G1 Z100
G1 X100 Y100
Explanation: Pause for 30 seconds, then start moving towards Z100, and move to X100 Y100 (regardless of whether we’ve arrived at Z100 yet or not)
Pause Method 2 Example/Description:
Use M400 by itself to pause until the next command completes
M400
G1 Z100
G1 X100 Y100
Explanation: Pause until we arrive at Z100, then move to X100 Y100