When we think of these as amounts of time/money/etc, they are singular: Six minutes is all I need. Ten dollars is all I have.By the way, are these sentences correct?
1/ six feet aren't enough for the measurement.
2/ players are playing nice now.
3/ four shops don't fit to assurance of quality standards.I am not sure what message you intend to convey with these unnatural sentences.
Student or Learner