Is it internal users calling extension 600 or is there an associated phone number that is being called from outside?

If it is outside callers, you can switch the destination based on night modes. If it is internal callers, you would need to use call forwarding.

For call forwarding, assign the virtual to a button for 604 and 608 in 15-07, then program that button to ring in 15-09. Then enable 15-02-21 on both 604 and 608. This will give you dial tone from the virtual, and allow you to dial the call forward access code.

If it is an outside caller, need to know what type of trunks you have (analog, PRI, SIP) as call routing is handled differently for different trunk types.

Thank you~
it is an outside caller，The trunk type is PRI, and the external call is answered by VRS first, using the voice recorded by 716+7+001, the external user presses 0 to transfer to the extension on duty, so it is not feasible to switch the destination according to the night mode

Maybe I didn't describe it clearly, I'll try again:
When the customer dials the company's phone number, nec8100 will be answered by VRS, and the welcome message recorded in advance by 716+7+001 will be played. At this time, the customer can directly dial the extension number, or press 0 to transfer to the extension group consisting of 606 and 608. For example, the group name is 600. My requirement is how to automatically or manually transfer the group of 600 to other extensions after 17:00 every day. When the user presses 0, the other extension will answer the call, because at this time Already off work. The CFW of the department group cannot be used, so I don't know how to deal with it.

I have tried to use the night mode to switch to the extension on duty at night, and recorded the VRS voice 716+7+004 separately. In the night mode, although the user can press 0 to make the night extension ring, if the user directly dials the extension is busy or unavailable If someone answers the call, it will still be processed by VRS 002 (busy) 003 (no answer) voice, press 0 at this time, still 600 groups answer.

You could use 600 as a virtual extension instead of a department group.

During regular office hours, when the VRS transfers to extension 600, it will ring on say extensions 606 and 608. At 17:00, they can then forward virtual extension 600 to a different virtual extension (example 700) which rings on alternate nighttime extensions.

Then when users come back in the morning, they can cancel the forwarding.

Thank you for your patience.
Could you please give a specific programming method, I am a novice.
For example: virtual extension 600 during the day and virtual extension 700 at night. After VRS answers during the day, if the customer presses 0 to transfer to the switchboard, it needs to ring at extensions 606 and 608 (requires circular ringing, not at the same time), and after 17:00, it needs to ring 700 ringing, how can the main station staff switch easily or set it to automatic switching.

You can do almost anything with mode changes on the NEC. Dept groups are VERY limiting FWIW. Question, this system in the US? Because it's weird to use the VRS rather than the AA here. Also only 2 extensions why circular ringing?