We currently do not have the provision to generate a tLOW of 24ns in push-pull mode at 12.5MHz as the duty cycle parameter has a resolution of only 10ns. Hence, you can specify a tLOW of either 20ns or 30ns.

Please do note that the minimum tHIGH value that must be specified in the software cannot go below 40ns. Hence, you can try any combination of tHIGH > 40ns along with tLOW of either 20ns or 30ns as per your requirement.