Sure, but it takes load from the db so if the token is long expired you don’t even need to check the db anymore. You’ll still ned to expire reserved slots independently from the client.
LostKobrakai
NobbZ
One could even sign the token with a :signed_at time.
That time could be written to the database and when looking for available solts, we look for all WHERE blocked_since < five_minutes_ago OR blocked_since IS NULL (well, actually I mean the SQL that comes closest in its semantic to my pseudo-SQL 
).
So no useless lookups or writes to “free” a slot.
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