Are you looking to make a a server that is only daytime and sunny ill show you all you need is 1 redstone clock and 2 command blocks first all all you need to make a redstone clock click the gyazo below to see how its done
http://gyazo.com/145d16d7b3c0a2c0601bebc556449108
When you have that setup use a redstone torch to get the redstone live and delete a peice of redstone and quickly replace it with another piece of redstone to make the clock live and constantly ticking.
Now you have the clock done you need to go onto the command blocks 
Command Block 1 : /time set Day
Command block 2 : /weather Sun
Thats All There Is To It , There is no lag caused to the server at all , if you fount this tutorial helpfull be sure to leave a diamond and post in the comments if you want me to do anymore tutorials