「昼食と夕食の間隔が長い」の直訳は The interval between lunch and dinner is longになります。
昼食 - lunch
夕食- dinner
間隔 - space, interval
長い - long
もっと自然な言い方だと
I eat breakfast at 7, I have lunch at 12 and then I have dinner at 9. There's a big gap between lunch and dinner.
...After I eat lunch I have to wait a really long time before (I have) dinner.
もしくは...I have a 9 hour gap between lunch and dinner になります。