Boot MacOS on external disk - default

[Demovx]

Hello!
I have a qestion.

I have iMac with usb external disk with MacOS High Sierra. ( No APFS ).
When i power up imac, i see black screen. After 10 seconds, the apple logo appears and the booting from the external usb disk. All works fine but i need boot default from external USB ( save the 10 seconds ;p )

My internal disk is clean - no MacOS On this drive.

Can i change in terminal or other app this setting?

In my settings> start disk> i have only my external disk. ( MacintoshHD macOS 10.13.2).

 

[Fishrrman]

Try going back to the startup disk preference pane and re-designating your external drive as the "boot drive".

I will guess that a "short delay" after you press the power-on button is going to be "the norm".
The iMac first has to check itself for hardware integrity, and then "poll the buses" to find the external boot drive. And then... start booting from it.

I've been booting and running my 2012 Mac Mini from an external drive for 5 years now.
Works fine...

 

[Demovx]

Try going back to the startup disk preference pane and re-designating your external drive as the "boot drive".

I will guess that a "short delay" after you press the power-on button is going to be "the norm".
The iMac first has to check itself for hardware integrity, and then "poll the buses" to find the external boot drive. And then... start booting from it.

I've been booting and running my 2012 Mac Mini from an external drive for 5 years now.
Works fine...

Hmm, if it's Ok and normal loading external disk 5-10 seconds that's Ok.