Originally Posted by
espoire
Just clip it. Managing MF clipping properly takes a huge degree of concentration to maintain, particularly in the presence of things like haste procs, pushback from damage, being under hit cap, etc. This is focus that could be far better spent on aiming Halo properly, responding to procs promptly and dealing with fight mechanics. By your own admission, you're new to Shadow. Leave the <1% DPS micromanagement to the pros.
So, yes, clip MF for subsequent MF casts. If you need to cast anything else, just cast it. Don't worry about MF's duration or next tick.
Exception: Finish MF (Insanity) channels that you're extending beyond the end of DP, and try to start a fresh one <0.5sec before the end of DP.