Here's what I tried
$ dateutils.ddiff 02:15:00 00:26:00
-6540s
$ dateutils.ddiff -i %T 02:15:00 00:26:00
-6540s
$ dateutils.ddiff -i "%T" 02:15:00 00:26:00
-6540s
$ dateutils.ddiff -i "%T" "02:15:00" "00:26:00"
-6540s
$ dateutils.ddiff -i "%T" "02:15:00" -i "%T" "00:26:00"
-6540s
Couldn't figure it out. Desired output : 01:49:00