Been having a lot of trouble with render times recently. I am running C4d on my Imac and had been leaving a scene to render over night.
The problem I had was that when I check it in the morning, frames that had started out rendering at about 9 seconds each, had suddenly ramped up to sometimes 15 minutes per frame in the space of one or two frames.
The weird part is that when I check on the render (move the mouse, click back on c4d) the render times return to the 9 second mark per frame!
I read some stuff about bugs with turning the screen off (no power button for the screen on imac, just old faithful ctrl+shift+eject) but even leaving the screen on all night seems to not have done anything.
what version of the OS and (probably less important what version of C4D)? Yosemite (or was it Mavericks) has "AppNap" which can be turned off on an app by app basis - supposed to save power with laptops on battery but not good for power hungry apps like C4D. Much earlier versions of C4D used to have a setting in the prefs to "Deny Power Cycle" so the computer couldn't go to sleep during render but that got more sophisticated a long time ago too... now it just keeps on rendering usually but it's been awhile since I had an apple display that can't be turned off. Have to guess app nap without any more info