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.
Confirmed in there are Primož Roglič, Wout van Aert, Steven Kruijswijk, Tiesj Benoot, Mike Teunissen, Tosh van der Sande and Nathan van Hooydonck, whilst Tom Dumoulin and Koen Bouwman are in Colombia in a separate camp.
Jumbo-Visma went on to race the Volta a Comunitat Valenciana without it's major leaders, but didn't have their lucks about as the team abandoned due to positive cases within the team, after David Dekker had already abandoned the race after a bad crash.