The OpenAPI definition of the duration format follows RFC 3339. The Kubernetes definition is more relaxed, which is nice, but IsDuration allows text that produces unexpected values from ParseDuration and unmarshaling.

https://go.dev/play/p/kZhy7fepBAM

I expected 1.5 hours to be 90 minutes, but this valid text is interpreted as 5 hours:

fmt.Println(time.ParseDuration("1.5h"))        // 1h30m0s <nil>
fmt.Println(strfmt.ParseDuration("1.5 hours")) // 5h0m0s <nil>

I expected 1.5 days to be 36 hours, but this valid text is interpreted as 120 hours:

fmt.Println(strfmt.ParseDuration("1.5 days")) // 120h0m0s <nil>
fmt.Println(1.5 * 24 * time.Hour)             // 36h0m0s