They can track us through lightspeed, and we only have so much fuel to outrun them
this is a math equation.
and don’t try to compare this specific aspect to TESB, where leia and han lose the empire relatively soon in the movie and just have to find a safe place to hide for the rest of the film. not run, hide. so no math was needed. TLJ, however…
but the ‘premise’ in TLJ is still the same as the one in TESB - it’s a slightly different version of this part of TESB’s plot.