The SCLK specification is tested with a 50% duty cycle, so that tCL=tCH. Also, limits are set not only using characterization data, but also with repeatability, correlation, process drift/corners, temperature drift, and an ATE guardband. In this case, think not of 45ns +35ns = 80ns, think 45ns + 35ns + rise + fall + ATE guardband = 95ns.