SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '3f68d50b8cb5178252829d2e42778d29612b9c218f4dcb3611a5782308b69367' 
  AND token = '+Jg/9VkjurwJuspOFJWMiPB4JdBAEBxHi2tskYlZ4f0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00026

JSON explain

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