SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '8251d56f8f97c4e7bb3f852786fae8e1556254e408f3f0a63ec8068b1ed0b91a' 
  AND token = 'aB5UrzwEpP7ekmFkKbjPih80cujWMkCbc65LJIH5xd0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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