If you speak the domain name, can someone type it in? If not, you might have a problem. If I say go to "Tommy24x7.com" what will people do?
Only one of those is correct. This willbe a problem if you ever expect people to respond to spoken advertising or word of mouth.
It's great for a convenience store neon sign.....
It's great to have 24x7 in National or other key words...for example..
In short 24x7 names are good when added to national or key-word viz. markets, funds, lottery, auction etc..