Slices on the octatrack are equal divisions (2 3 4 6 8 12 16 24 32 48 64) of the total length of the sample. So the tempo doesn’t really matter, just the spacing of the sounds in your sample.
When I’m playing a samplechain of single hits I turn timestretch off…
samplechain of drum loops or something timestretch on.
Do a quick scroll through the forum and you will find a ton more info.