Does jumping to a nebula still slow the rebel fleet if they're not yet visible in the sector?

It's not unusual to find a few nebula beacons in non-nebula sectors. These apparently delay the rebel fleet's advance when you visit them. It seems like they always end up clustered right around where I start in the sector, though; do they still delay the rebel fleet even if the rebel fleet hasn't (visibly) arrived in the sector yet?

Alternately, how many jumps does it normally take before the rebel fleet appears in the sector?

Solution 1:

Normally the rebel fleet appears after your 3rd Jump to normal sectors. If you jump into nebulas you will still slow the fleet down. If you only jump into nebulas from the beginning it takes them 6 jumps to arrive at the sector.

Yes the nebula slows down the fleet even if it is not visible.