SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '550f68b71e5e5d83a91c6f16233314635bb0e21b722021ff958dae7f89943840' 
  AND token = 'j/bT9V+Ln2lwdS9GQ+KFTngooEE6k7mGgHicaEecZBk=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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