[formerly_proven]

CRTs did tend to take a couple seconds to properly warm up, charge up and reach final image size (the image is directly scaled by the acceleration voltage, which is a high impedance source charging a not-so-small capacitor formed by the aquadag on the inside and outside of the picture tube).

[catalogia]

CRTs did need a moment to stabilize the image, but they showed signs of life virtually instantly. At the least they'd make a little noise and had buttons with tactile feedback so you knew something was happening. Many screens today have capacitive touch buttons and have 5 seconds or more between a button 'press' and anything happening at all, leaving you to wonder if you even managed to successfully press the power button in the first place.