In fact yes with source edit it is possible and easy to it is very easy to set up (all in game.h and game.cpp). Depending what you need you may just adjust the these vars ( lightHourDelta, lightHour, SUNRISE, SUNSET) to change the lenght of day/night and these constants ( LIGHT_LEVEL_DAY, LIGHT_LEVEL_NIGHT) for the light level. In the project I'm coding for we needed variable light level depending on event and variable lenght for day/night so I added custom lua function. It works and doesn't affect the player "internallight" as Cykotitan mentionned. It's also easy to add a global event to this so you may use it as trigger in lua code.
(I gave you all the needed information so don't ask for a tutorial, if you do a little work on your side you'll be able to implement this in your ot too)