I can give you several sentences.
These avocados are only seasonally inexpensive.
Seasonally
some dogs that shed seasonally are bernese mountain dog and border colllie.
No. Koalas do not change colour with the seasons.
Yes they migrate seasonally
Surface salinity in polar regions varies seasonally due to the formation and melting of sea ice.
i do not know how to use embalming in a sentence. (there is the sentence)
Mesapotamia flooded seasonally.
monsoons
huracan
huracan
Average U.S. unemployment duration as of October 2009 = 26.9 weeks (seasonally adjusted) and 28.1 weeks (not seasonally adjusted)
So- you are asking when to use 'when' in a sentence. When you are asking how to use when in a question, you are already using when in a sentence, because a question actually is a sentence. I like to use when in a sentence whenever I like.