SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '0351c5092c743146cc6d279f6eca1f12398a39c5080215f213d6c75822d02500' 
  AND token = 'LXFKti2PVrCxEKkJAVxj+yLniEdxRWSBwuPOqfudmTA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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