This quote, "Prior to the start of the gibberellin treatment, the plants were allowed to reach an age at which they were fully capable of responding to thermo- or photoinduction." from
https://www.ncbi.nlm.nih.gov/p... suggests that gibberellic acid does not affect the timing of the transition from the juvenile phase (unable to flower) to the mature/adult phase (capable of responding to the environmental triggers to flower) but affects the requirement for environmental triggers for flower initiation. That would not apply to daylilies as they do not have environmental thermoinduction or photoinduction requirements to initiate flowers.
