you don't have to play with light schedule. A photoperiod will never flower under 18/6 schedule - never.... nor 16/8 .... 15/9 starts to get into a grey area and not all photoperiods will flower under 14/10 but some definitely will. We use 12/12 to guarantee to cover rare genetic oddities.
if it started to flower in 18/6 there is no rational reason to believe it will stop.
The length of uninterrupted darkness is the cause for bloom phase to start. It is a hormonal response in the plant. The hormone is only produced in darkness, hence the need for uninterrupted darkness for flower to start. If enough accumulates, flower phase starts.
This absolutely does not accidentally or randomly turn into an autoflower without a fairly complicated multi-generation interbreeding process with a 'ruderalis" plant that is not a photoperiod plant, lol.
RQS lied to you and were smiling while they did it.