How much are scenes from syndicated old shows cut out for commercials?

I have heard of them cutting whole scenes out but do they also cut out
just snippets of dialogue at
various places in the show in order to squeeze in an additional
commercial?

Uniblab...

Yeah, they sometimes do the dialogue snipping instead of/in addition to
scene cutting. I remember that the last time "All in the Family" was in
broadcast syndication, all kinds of lines were snipped within scenes. Very
annoying.

Jon Purkey...

One day I compared my Green Acres DVDs to the episodes shown on TV
Land to see what scenes had been cut. I was really surprised to find
how they cut lines so that one character was responding to something
else said instead of the way it was originally. That really turned me
off to watching edited shows. Prior to that I had assumed they just
cut entire scenes or cut sections of scenes.

And as annoying as the line editing is to viewers, the people involved
in the creation of the shows must get really irritated by it. There is
no indication that what you are seeing is different that the way it
was meant to be.

At least American Life isn't as bad about the editing. Some hour long
shows like The FBI run about 48 minutes without commercials and some
half hour programs like My Favorite Martian are anywhere from 22.5 to
24.5 minutes. I record to DVD-RAM so can edit out the commercials to
check the length. Not sure if that is unedited, but it's better than
TV Land and other networks where it is usually 22 minutes for half
hour programs and 43-45 minutes for hour programs. American Life still
seems to have as many paid ads. What AL doesn't have is a lot of
promotions for other programs and other non-ads like the Retromercials
on TV Land that take up time from the show and don't provide any
direct revenue to the network.

I was watching "Amen" on the "I" network last night and I swear they
cut out Deacon Frye's
dialogue in one scene because another character responded to him and
what they said
had no relation to what the Deacon had said just moments before.

telenovels...

It varies from show-to-show. And channel-to-channel. Old hour-long
shows in the 1950s/60s used to be 51 minutes. Example: Outer Limits.
When rerun, they are chopped down to 45-46 minutes.

Later 1970s/80s/90s shows like X-Files were originally 46 minutes, and
they are either aired as-is with no cuts, or trimmed to 42-43 minutes.

Current shows are already 42 minutes long so they have no cuts.

Another method used by Spike Channel is to skip every 15th frame,
thereby speeding-up their Star Trek reruns to make 46 minutes fit
inside 43. So nothing is lost... it just runs faster.
.

Cuts don't bother me. I find that older shows often had a very, very
slow pace, and so if the cuts are handled well, the faster pace will
actually improve my enjoyment. (Example: Old Outer Limits or Kirk's
Star Trek.)

They might have done this throughout the show but that is the only one
I caught.