It depends on the type of phytochemical or other constituent you are interested to extract. The temperature is an important parameters as majority of phytochemicals are thermally labile. Therefore, it suggested to look for the thermal stability of compounds before selecting the extraction conditions. The second thing is polarity and solubility of compound of interest which forms the basis of selecting the extracting solvent. The polar compounds can be ideally extracted with water or hydroalcoholic solvents.

For hot water extraction, you can opt for reflux/distillation assembly

There is no hard and fast rule for hot water extraction. It depends on the nature of constituent you look for. You have to standardise your own method of extraction in each and every case. Or else act according to the literature. 

As you mentioned 4 hours or 8 hours has to be fixed by working out on the quantity of metabolites or the yield of extract obtained.

However to perform hot water extraction it should be done with reflux condition and adequate stirring is also essential to ensure complete extraction.

Thank you for all the answer..the reflux method is using soxhlet apparatus right?

For hot water extraction, reflux cannot be done through Soxhlation. A three necked  RB flask with stirrer at center neck and condenser at adjacent neck will do it. You cannot do it in soxhlet apparatus.

All the best

thank you very much for the respond