Hello let me answer your question this way,
Most varieties of watermelon takes 80-90 days to mature eg. Sukari F1, Zuri F1 etc
Watermelon performs better in warm temperatures/regions about 30 °c at fruiting time
For larger fruits and high sugar concentration at fruiting stage their should be low soil moisture
Cold conditions should be avoided at all stages of growth. So these guidelines can really help you depending on where you're and prevailing weather pattern in the next 90 days. Thanks