Then just enter in the callsign of the airport (COF in this case) and you will get some results with links to 1 or more PDF's. The one with a number in it will take you directly to the page for the airport you are looking for.
Here it is for COF (link may not be valid as the date may have changed) https://aeronav.faa.gov/afd/21may2020/s ... AY2020.pdf
In that PDF there is text like this that states the airspace hours in Zulu time:
Just convert that to standard time to get the hours in your area (lots of online calculators for that)AIRSPACE: CLASS D svc 1300–0500Z‡ Mon–Fri, 1400–2200Z‡ Sat–Sun, clsd hol, airfield clsd third Fri of month; other times
Also, It is a good idea to call the airport to make sure they are closed, as perhaps there is a special event, or they are closed for longer for a holiday. The airport manager number is also listed on that PDF.