You should take the time to do this well.
Which verb would you use for 'take' here?
Debe tomar su tiempo para hacer esto bien.
or if it's more of a command: Tómese su tiempo ..... Take your time ....
In my opinion:
Deberías tomarte tu tiempo para hacerlo bien.
I hope this helped you.
About 1/2 way down the article it discusses taking the time. I would have suggested gastar. Shows how much I know.