SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '503df8db8feae6375a4d493dcb15a3043069456a0931afc91b484df5f0103920' 
  AND token = 'hilbqu8LMryXoL4FHgTqVxdrNPrvVw5Ytwt7XzgXUs0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00026

JSON explain

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