When referring to a certain time after a previous event, we often use the phrase "nine hours later on". However, there are several synonymous expressions that can also convey the same meaning. For instance, "nine hours after", "nine hours elapsed", "nine hours gone by", and "nine hours past" are all frequently used alternatives. Other possible options may include "nine hours further on", "nine hours down the line", or "nine hours henceforth". In general, it is always a good idea to vary your language so as to avoid repetition and add richness and depth to your writing or speech.