SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'e8c0248adafdb4f805287679551d5b35a937ce932badb03555cc2ecd57259138' 
  AND token = 'Lxsr0jT8hgFP8eb6ov+hYTs7NcfLIMPHcuT293+GbFM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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