Help calculating time until

Hi please could one of you whizz kids help me out
I have 4 fields in my database all logging time
time1, time2, time3, time4
I can get the number of hours and mins between time1 and time4 and also time2 and time3 which is exactly what i need, however I need to addone result to the other and display the result
I need to work out and display the following
{{time1.timeUntil(time2, true)}} + {{time3.timeUntil(time4, true)}}
this outputs something like this 00:00:0300:00:03
but I need it to output 00:00:06

Is this possible or am I barking up the wrong tree