Hebrew is not an exact language, nor is it precise. And Genesis was written in a very ancient Hebrew, which was what we might call proto-Hebrew, which had far fewer words than later Hebrew.
. If you use an inter-linear Hebrew-English version you will probably be surprised at how differently it comes out compared to an English 'translation' which regularly has to interpret idioms. You will also be able to note how yom is used in a number of different ways. Thus it is true that Hebrew is lacking in descriptive words. Hebrew is based on its verbal system because the Hebrews were a 'doing' people. The whole language is based on its verbs. Interestingly they have no tenses which signify past, present and future. Their verbal tenses reflect completeness and incompleteness. Their prepositions are relatively vague.
In fact Genesis 1 makes clear that yom means 'a period of light'. It actually SAYS SO, There are no grounds there for making a yom a 24 hour day. It is pure dogmatism that seeks to do so.