As I was discussing and proving that IMHO Perez had nowhere near 20kW penalty on his ICE, I ended up being criticized for missing wake effects and more. So I decided to lookup some telemetry to figure out the effect on following behind another car:
LEC v VER telemetry at the start of the race, top speed is the primary indicator for slipstream of course, you can check it at either straight into T11 (longest) or into T17 (shorter), each lap has a given gap between VER in front and LEC behind, no lapped cars or other slipstream/DRS was around for any of these laps:
<1s: https://i.imgur.com/DHbg2gj.png
<2s: https://i.imgur.com/DhK5jiB.png
<3s: https://i.imgur.com/yjd92Tt.png
<4.5s: https://i.imgur.com/V2Zedxt.png
<7.5s: https://i.imgur.com/s9XJNOa.png
In practice at 3rd graph there's no more slipstream and that's around 2.7s behind. The 2nd graph has less than half the slipstream effect of the 1st, and that's 1.5s behind roughly. So I believe there's basically no significant slipstream effect beyond 2s and even at beyond 1s it's relatively minor.
One can try to look into the fast corners in S1 too, and there the only graph with disruption is the first one and that's 0.5s behind at end of lap, Verstappen had just passed Leclerc, and even there I'd argue that on T6-7-8 Leclerc is already able to take more speed in the corner.
It does seem to me like these cars can indeed follow pretty closely even through fast corners without losing too much, and the slipstream effect has shrunk significantly to almost disappearing after 2s behind.