Flare Networks has released a visual guide to claiming Spark.
Snapshot date: 12 Dec 2020
This date fixes all the balances to the XRP account
Self Custody Claim Deadline: 11th June 2021
This is the deadline by which self custody XRP holders can claim the Spark token. You have until this date to setup your XRP account with the MessageKey
Expected Q1-Q2 2021.