If you are referring to cell respiration, then yes, you are right that plants need oxygen at night as well as during the day. Gasses like O₂ and CO₂ pass in and out of plants through stomata which are pores in the leaves that open and close to regulate gas flow. Usually, these pores are closed at night to prevent water loss, but they aren't sealed perfectly and some plants open their stomata at night in fact (cacti). Gasses are able to seep into and out of the leaves at night under normal circumstances. This is how O₂ diffuses into plant tissue.

Plants have holes in their leaves called "stomata" which open at night to take in oxygen. They open primarily at night because during the day, they would lose too much water from evaporation. When it is cooler at night, they open these holes to take in oxygen. They still have respiration during the day (the holes are slightly open), but they primarily photosynthesize in the day.

Plants have pores in their leaves called stomata, which they open up at night in order to let the air flow into the leaf. Leaves contain spaces inside of them that work similarly to lungs.