According to the wiki:
Right now, my nametable updating routine (used for vertical parallax) updates a region of 4 x 8 tiles and takes around 258 cycles. I'd like to increase the size of the update region, but doing so will obviously increase the cycle count as well.The NTSC video signal is made up of 262 scanlines, and 20 of those are spent in vblank state. After the program has received an NMI, it has about 2270 cycles to update the palette, sprites, and nametables as necessary before rendering begins.
Assuming I perform sprite DMA and overwrite the palette with a 32-byte zero page buffer each frame, approximately how many cycles can I safely budget for nametable updates?