I'm trying to learn War Pigs by Black Sabbath.

In the bridge, the drummer marks the first beat of last bar of a section by using the hi-hat, som tika-tsheek sound. Each of these sections consists of four bars where in each of them Ozzy begins a new verse. The section begins with a powerchord slide.

This can be heard in for instance after bar 17, after the intro:

This can be used for timing fills, before doing a power chord slide that begins on the first beat of the first bar after the "'hi-hat bar" (turnaround?). So I wonder:

1. Is this "hi-hat thing" called something? I both wonder what the stroke itself is called and the type of communication it seems to be.

2. Should I time the fills with regard to this "hi-hat thing" or should I do it in relation to the song? The singer could always be a bit off so I guess it's better to go by the drums?

3. I want to practise my fills in relation to a slower drumbeat. A metronome won't do as I like to practise listening to the hi-hat and time after that. So is there some Android app/Windows software, that you would recommend for such task?

Any article, video instruction or similar on the subject is very appreciated.
Windows media player will allow you to slow down songs.
EBMM Bongo HS 4
EBMM Sting Ray 5
Eden D410T
Tech 21 Sansamp RBI
Tech 21 Sansamp RPM
Art 341 Dual Channel EQ
QSC GX5 Power Amp
It's called an open hi-hat, because the hi hat pedal is lifted to allow the 2 cymbals to jangle and vibrate off one another instead of "closed hi hat" which is when the cymbals are held tight to supress vibrations.

The rest of the hi hat strokes are performed by depressing the hi-hat pedal on the beat. The drummer strikes the cymbal on the off beat when the hats are in the open position, and closes it on the beat to create this sound at the end of bar 18.

He does it to create a more interesting rhythm than just "ts ts ts ts" over and over, and also to communicate the timing with the rest of the band, as you've noted.