This means first search is after 1h, second after 2h, ... until the time reaches 7h where it stops getting longer.
...
So - does it get back its sources after several hours?
I cannot be sure, since 7h is a VeryLongTimeIndeed (TM)

But:
A few times I left aMule working when I'm out-of-town for work (or vacation).
Last time has been this weekend (I left aMule working ok Friday ~5 PM and came back shortly before sending prev message i.e.: Sunday ~7PM)).
Almost each time I found all my sources at 0.
I obviously cannot know exactly when they went low, so I cannot know if it is >7h, but they looked pretty stable.
If I'm in front of the PC I usually do not wait 7h before acting

The 7h timeout is per-file?
In that case I could let one of the files alone (when I see sources going to 0) for >7h and see what happens.
... or should I leave the whole bunch of downloads alone for a whole day?
In any case I would suggest to restore the timeout to 1h (or even less) if the sources count drop to 0.
Rationale behind that is that for rare files, possibly with feeds not always online, the net overhead is more than balanced with the chance to find another possible source before it goes offline again.
Thanks for the insight.
Mauro