4-5 hours is quite common for folks that need to juggle work and run lol. Unless you don't need to work,you can have your 7-8 hours of sleep daily ah.If sleep late and/or wake up too early with only 4 or 5 hours sleep, will u all still proceed with long run? Or give up, try to sleep more?
That being said,it's all about how your body feel. If it's a easy run or lsd,I will normally proceed. If it's those kind of threshold,intervals,progressive Long run,I may not.