Do DOKODEMO Points expire? How long are they valid for?

Yes, DOKODEMO Points have an expiry date and it will depend on the type of Points.
Regular Points expire 360 days after they were credited to your account.
Limited-Time Points earned through promotional events or campaigns usually have a shorter expiry date and vary between promos so be sure to check the promo details at the time of purchase.
For more information refer to this page:
What are DOKODEMO Points?