Basically all computer monitors need at least 5 seconds to turn on. My iiyama G-Master GB2888UHSU monitor needs 10 (!) seconds to switch on from off-state and on waking up (from sleep mode) it takes 8 seconds. This is driving me crazy as I want to save energy but I can't settle with a startup time this long. So I turned off sleep mode and just keep it on all the time. I'm aware that my model is even slower compared to most other monitors, but others still take quite a long time.
Also note that smartphone displays, car headups and even notebook displays are significantly faster.
Why is that? Are manufacturers simply too lazy when it comes to optimizing the boot time of their monitor operating system? Or does it have a real technical reason?