Start with two to five minutes, not twenty. Most beginners are told to sit for long periods and then conclude they are bad at meditation when their mind wanders. The mind wandering is normal. Noticing it and returning to the breath is the practice, not a failure of the practice.
Anchoring your practice to an existing habit makes it far more likely to stick. Five minutes of breath awareness after your morning tea, or before you open your phone, ties the new practice to an existing cue.