Usually it would be before the Grand Tours, and some other races, but nowadays you will see professional cyclists riding up and down the Teide volcano almost throughout the whole year.
It's been a popular destination for a very long time, the good weather, infrastructure and a wide variety of climbs makes it a very attractive option for teams looking to do training camps, specially with the proximity to mainland Europe.
Jumbo-Visma are part of the field who's currently training on the volcano as they have most of their leaders preparing for the spring where they will be fighting for wins all across World Tour calendar.