Dear Carlos,
If you have the number of days since germination, the average planting period, and the weather data, you can estimate the heat units required to reach maturity and use that value (plus 100) as potential heat units (PHU) in the management file.
About the photoperiod, the crop growth model in APEX does not simulate processes like flowering, where the photoperiod plays an important role. It can simulate a winter dormancy regulated by the day length, and it can be adjusted using parameter 6. What other processes were you considering as affected by photoperiod?
Best,
Luca