SUMIF - Time Duration Issue?

[JoshEvo]

Hello,

Attached is a spreadsheet that is recording machine downtime.
As per summary table inserted above the data in the first 4 tabs (we are focussing on A, B, C and D Service downtime). I would like to retrieve total downtime within each month.

Sadly I haven't been able to figure a formula that totals the time duration in column F (Total Down Time) as I believe it has transferred into excel as an incorrect format.
I have tried formatting to [h]:mm:ss, however this doesn't seem to fix the issue.

Any help greatly appreciated!!