Clicking on a date and setting up the lighting usually works along with not saving new sessions over the currently set time and date, and everything should remain fine. I did that with my routes because I'm not interested in autumn or winter routes. I have plenty of cold weather to contend with and enjoy the warmth, well not this year because there was too much of it, of the summer months.
Thankyou for your replies,,, the thing is, it takes me that long to build a route that now a lot of the trees have changed cokour and it keeps getting dark and I just wanted to freeze it all until I had finished.
Len
That is because the date (and season of the year) in the Environment Tools will be automatically taken from the system date stored in your computer. It usually takes me 12 or months to build a route so I see some of the trees changing as well. It never bothers me but one solution you could use is to go into the Environment Tool Location control and manually set the date to a month that matches the season of the year you want to see. Then save the route so the date will be set to the one you have entered.
Time is stored in the Session using the two rules I listed in my first post. Normally Trainz will default to 10am in a route without a Session.