SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b2be399c0e8d811904cd17eaf2823f7d68cdd1afbf20d3d619cb34dba4d29a62' 
  AND token = '/NsRU1tUrBpFZ6ZZry5XmiZKl6wK8f0fPg8MStTV2lg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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