To have a 24/7 server you must buy a server. A few companys are Daddy Cheese and Global & hosting. They will give you help on plugins and they have good support. Servers can be only like 5 pounds a month for a decent server.
download Minecraft Server from the downloads page on Minecraft.net. Port forward your router. Leave your computer on 24/7
this, combined with an old computer you found at a garage sale or something, means you can be on your free server 24/7 with virtually no lag. Just run the server on the junk PC and connect to it normally.
Private Mod Note
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[INSERT OBLIGATORY "CLICK THE GREEN PLUS BUTTON IN THE BOTTOM RIGHT-HAND CORNER IF I HELPED YOU"]