SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51c0d416e3c82f94c02cc01460f167887db720ff9e8b4a32eedc0411a2f3db19' 
  AND token = 'zevaakBAe2nO5dOXwcIjQQmKShQq/AzOt1IsjrI6BpI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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