U.S. Flag Code notes that flags can be flown 24 hours if properly illuminated during the night hours. This can be interpreted as a specific light shining on the flag or as an ambient lighting source in the area that has a good light spread on your flag. We recommend ground lighting installed away from the base and spot lit on your flag(s). A high lumens white light is best for showing the true colors of your flag(s).
The code also notes that flags should not be flown in wet and inclement weather. However, this was written at a time before flags were made out of long lasting weather resistant materials such as nylon and polyester. With the all weather materials available now, it is perfectly OK to fly your flag 24/7. We do though, recommend removing your flag(s) from the flagpoles in times of high or heavy winds to reduce the chance of your flag failing prematurely or damaging your flagpole.