SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '790e03c1ec8b5bb55accf3c78954d7106336557407960bb8a076c1b34bbc48bc' 
  AND token = 't685vyvBRGSAqkK4ZnWdAhbKB0wtKuEEXYjH1OjrR+4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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