Translation:They will have dinner at 8 on Saturday.
No because that sentence is a very general and almost robotic statement saying "they have dinner on Saturday at 8". You add 会 to write the sentence in the future tense "they will have dinner..." Though I'm not a native Chinese speaker I'm only speaking through observation so maybe someone who knows better can confirm or deny.
I'm curious about the sentence construction. It is [they] [saturday] [will] [8:00] [eat] [dinner]. I expected [they] [saturday] [8:00] [will] [eat] [dinner]. My take-away from previous exercises was to keep time elements together and order them big-to-small (year, month, day, time).
Question: I put "they can have dinner at eight o'clock on saturday". I was imagining trying to arrange dinner with friends. So I can imagine my partner saying that to me while she's on the phone with friends as we're trying to arrange a time. Is this correct?
I'll remember for future tests that DL is emphasising the "will" sense of 会