nah, if you're wondering bout sumthin like DotA, they have another spell that does nothig, then they add/remove eng upgrade when the time of day becomes night/day
I m not sure it will work but there is another possibility: make some special dummy for each player on day or night and add requirement to spell to this dummy. So, if you have day-dummy (time 6-1 you can cast some spells. If time comes 18:00 kill that dummies and make different night-dummies.
Im not sure it work with abilities, but with construction it works. You can try it