SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51829ebab2cd3ce63737ca58ff7ac5cb6b84979bebc8b890d07bee978cb982c6' 
  AND token = '89WEbOnv/wWcKwfRnX3n+bNlMU4fgK4qn9UC8Hzt9i0=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00031

JSON explain

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