this is basically how if you want to do say.... a fish out of water time travel story you've got to set it at least over a curtain amount of time in the past which seems to be between 20 and 30 years.

This is presumably because between 20 to 30 years is the minimum amount of time it takes 1)values and lifestyle to move forward enough to be really noticeably different to most people 2)for a time in past to be assigned an amusing stereotypical aesthetic that most people will recognise

Examples

film

• Back To The Future: 1985-1955

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Live action TV

• That Seventies Show debuted in The Nineties and was a big hit. The producers made another series called That Eighties Show that debuted in the early Naughts, which bombed.
• The "Stargate SG 1" episode "1969", which aired in 1999.

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Examples (aversions only)

film

• The Queen which showed how attitudes to royal family where different a mere nine years before it came out

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Live action TV

• about half the flashbacks in Cold Case

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