Are there any issues I might experience if I leave the mirror up on my DSLR camera for a long time? My use mode would be "live view" mode connected to AC power, and using the HDMI output of the camera to a capture card to record raw 1080p frames to a computer. In this mode the mirror seems enter the "locked up" state for as long as I record and also the on-camera display turns off and then the mirror doesn't drop until shortly after I stop recording. So far I have only recorded for a few minutes at a time for testing purposes but I want to set up a possibly months long project where I record a time lapse in this mode. Assuming the camera is sufficiently protected from heat, moisture, etc. would there be any issues including potential damage to the camera with leaving the mirror locked up for this long? I know that my camera requires power to hold the lock up, so this may be a question of if the electromagnet or solenoid or whatever is rated for continuous use, but I have no idea if such a thing is known outside of the engineering team that designed a particular camera.
I had the thought of simply taking still images, but this is sub-optimal for several reasons: first, it's only possible to take a maximum of 999 pictures in a set using the built-in intervalometer, and I would be capturing something like 30,000 frames per day. It would also require extra workflows to frequently swap out memory cards, shuffle files around, and turn images into video, not to mention re-compression. This all needs to run mostly unattended.
Ideally I would like to use an old DSLR I'm not using for anything else for this project. However, I'm interested in this question for DSLRs in general, in case for instance older DSLRs are more (or less!) prone to some failure mode from leaving the mirror locked up for too long.
If it makes any difference, I'm not planning on shooting in a direction that has light from the sun directly (e.g. not by reflection) entering the lens at any part of the day.