The device is under full load for about 10-20 seconds after desktop appears and it takes a while for the services to reply to the battery and governor requests.

When ASUI is started, the brightness is set to the last value you set it to. If the slider doesn't match the brightness of the screen then you probably have the ALS filter active and it doesn't work well with the advanced-brightness code used in ASUI.

Scroll down to the "volume and brightness control" section on the about page for instructions on disabling ALS on the n810. This also fixes the left thumb brightness problem.