It's not clear what you're trying to produce here, but if you're trying to detect ranges, you could do this:

if ($start_minute < 7.5) {$start_minute = .0 ;}
elsif ($start_minute < 22.5) {$start_minute = .25 ;}
elsif ($start_minute < 37.5) {$start_minute = .5 ;}
elsif ($start_minute < 52.5) {$start_minute = .75 ;}
else {$start_minute = 1.0}
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