SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '39840a373a828039021cca6821f74381242d0884f463bb598de41e5cdbebddc6' 
  AND token = '6+eNN9PKwbqUg7/L1JRSgWusIW11EmR/B8+L4lpgdKg=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00019

JSON explain

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