Time is key in medical treatments requiring the patients to undergo unpleasant sensations. This paper examines how virtual reality (VR) could be used to manipulate treatment time, with specific regard to chemotherapy. After reviewing the relevant literature, the paper focusses on «flow» as the optimal temporal condition to be created in distressing medical treatments. Based on the Dynamic Occupation in Time model, it argues that VR applications may induce flow when expressing appropriately high levels of novelty; complexity; skill demand; user engagement; and focus on activity. Lastly, the paper discusses VR applications meeting these requirements and suitable for implementation in chemotherapy.