Yes, timers are used a lot in our house and they do help.

Also, when practical, we give DD more responsibility. "Dada will be leaving to go to X at 10:30. If you want to come with him, be dressed and ready at 10:25." (Only works for kids who can tell time, obviously.)

Also, we use the RoboParent technique.

Can you come and get dressed now please?
I will when I am done with this?
Come and get dressed now, please.
No, I am going to write the whole page and THEN I will come.
Come and get dressed now, please.
No, I am not! YOU go and get dressed! I am NOT coming!

Act bored. Don't engage. Don't get riled. (That's the hard part!)