Hi deepak
Actually if you set a time which is in future or after the time whether you made the software for your target, then everything is fine. But as in your case, if you set up a time which is in past, then the system time is reset by systemd to the time when your software image was made. This is a feature, since you cannot go back in time.
However the RTC time ( hwclock ) will be the one, which was set by you and could be also in past. If you need to set your systemclock absolutely to past, then you can set up a time using the timedatectl ... command and on startup synchronize the system clock to RTC using hwclock --systohc.
best regards, Jaski