This is messy, so let’s clean up a bit

proper time: time measured by a clock at rest with respect to a specific observer  clock at the fastest possible rate
proper length: length of an object as measured in its own rest frame  largest possible length
time and length in other inertial frames can be calculated by the so-called Lorentz transformation (i.e. multiplying with or dividing by the boost factor )

proper time: time measured by a clock at rest with respect to a specific observer  clock at the fastest possible rate