When flying from Delhi to Nantes, the time of day you decide to fly out makes little to no difference towards the overall price you’ll pay on tickets.
The rainfall in Delhi is generally more than the rainfall in Nantes. This will continue over the next 5 days.
You can imagine temperatures to be in the 40 °C range in May. The weather in Nantes is generally colder than Delhi's. As flight availability is subject to become more limited as peak season approaches it is ideal to book in a timely manner.