SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '857897cbef7493ea752efd1ed21fecd3da0e7f5d874d7193589818f8861ebe75' 
  AND token = 'Z5bHkM/RHdvoOwnIOKTNwOPsyD7zbzi+Hjn/d8qyI5A=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00023

JSON explain

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