SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a3947655a2e23007c4abeead0184546b77b4e5871a2e4d98d2947feacfdceabc' 
  AND token = 'HDEMkR4NYHEoMTOP7pRRbM8TuhusCP5pyvffPlCr+cU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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