How to use the Speed Feature in Premiere Rush on a Mobile Device

when i do this my videos gets laggy even when i export them :(

Trying to learn to use the speed option in one area of my video and use it at another area within the video. Does it only allow me to use the speed feature once in a clip?

Schweet!
Been waiting for this, thanks team!

So excited for this - timelapse here we come!