Timeframe question

Hi,

it might just be my lack of skills but how do i set a custom timeframe in a dashboard?

I have created a dashboard showing core performance values to one of our teams, and they have asked if they can get a view showing the performance the last 4 hours.
But I can’t choose to set a custom time frame.
I have tried just to change the setting in the json, but that just gives an error.

Am i missing something?

Regards

Jan L Dam