SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b8cd6133ebc02702799deef64de8d4b97f5f7a3cd93c8a61dbdec71e757435db' 
  AND token = 'UrYJu3lk4j/gxAtPzUKoxdVAFlCFMDIE7HXJuZKJbwI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}