When limited to VFR, which I often am for some of the aeroplanes I fly, I tend to think in terms of time, not distance for visibility limits.
5 minutes is a reasonable figure for local area flying _ in a 60kts microlight that is 5nm. In a moderately sporty light aircraft it's 10nm.
For cross country I might double that to 10 minutes.
Change numbers to suit your flying style snd confidence, but it's a reasonably workable system.
G