The reason solo mining isn't a good idea today isn't because the network hashrate is soo high. The reason is because the difficulty is too high for a gpu to hit a block in a reasonable time. Therefore regardless of when the miners stop, be it just before a difficulty change/just after a difficulty change, the difficulty is still way to high for your gpu to hit anything. the blocks will halt and nobody gets any block rewards, nobody gets their transactions confirmed.
This is exactly true. It takes a lot of time for the network to decrease it's hashrate rapidly.
