Junos device can only work as NTP server when it is synchronized to the external NTP server. This is by design, to protect you from situations where local time drifts significantly from "real" time, over large time intervals, due to small difference in clock rate. It is assumed here that external server is connected, directly or via other server(s), to stratum-0 clock (atomic or satellite system).
The pool.ntp.org project is a big virtual cluster of timeservers providing reliable easy to use NTP service for millions of clients.
You can get the router sync with the public NTP server or a imple ntp server application for windows will suffice the requirement…
Configuring the Router or Switch to Operate in Server Mode
In server mode, the router or switch acts as an NTP server for clients when the clients are configured appropriately. The only prerequisite for “server mode” is that the router or switch must be receiving time from another NTP peer or server. No other configuration is necessary on the router or switch.