Is there a way to change default start frame on the timeline? I would like to change the default start frame fro 1 to 0, so that I wont have to set the start frame at 0 every time I open up blender.
Open Blender, allowing your default startup file to load (so don't open an existing file).

Set the start frame to 0.



Save the file as your new startup file. Frame 0 will be the new start frame for all  new files created this way.