Yeah, I'm interpreting this as instead of sending an integer of the tick that something occured on, they're sending a floating number of when it happened.

I assume the float they send will have a limit in accuracy however. So really it's not like ticks are 'gone', they're just getting much much smaller.

The ticks aren't going away. They're just sending exact timestamps for movement so the server side view of a hitbox is more accurate when rewinding hixboes. The difference on 60 tick was sometimes large enough to miss headshots on faraway targets. It'd of course help if their clock sync and anti-drift measures were better now. It's NTP hard mode.

Is there a reason you would expect them to use floats here instead of fixed-point? I would naively guess the latter.

They just meant that things now happen within fractions of a time slice, instead of always landing on exactly 1/60th of a second boundaries.