Ive tested it on a copy of latest master without any customisation and cannot calculate hours using a computed attribute.
I am using io449 sent from Teltonika devices as my hours and it worked prior reordering of the handlers.
See image of the more view showing io449 in seconds and also see image of the computed attribute showing the value when tested but the hours are showing as 18 minutes.
Ive tested it on a copy of latest master without any customisation and cannot calculate hours using a computed attribute.
I am using io449 sent from Teltonika devices as my hours and it worked prior reordering of the handlers.
See image of the more view showing io449 in seconds and also see image of the computed attribute showing the value when tested but the hours are showing as 18 minutes.