Too Fast to be an assassin?

It's free week, so I've been playing a lot of games with her (srsly, 10 games in one day) and I noticed, that sometimes when I Q, then R + E, I'll E before the mark actually lands, so I can't explode it. is a very bursty assassin, but how can I burst them down quickly, if it's not ready to explode when I'm ready? imo this should be made so the mark is instantly set on the target.

On a side note, Can the Notification on the buff bar for her Twighlight Shroud(W), become a countdown, so we can know when the shroud ends? this can help us make plays. thank you