It depends how much you want to pass on your knowledge to others. Do not underestimate how badly paid instructing is. If you have independent means of support then you will get more flying if you make yourself available full time. Pay in the winter months can be as low as £500 per month take home.
Be careful which clubs you choose to instruct for if you go part time. Those with a large number of full-time instructors will give priority to them when taking bookings, and the initial assumption will be that you are prepared to sit by the club phone waiting for it to ring and pick up any scraps.
Having said all this, instructing has given me 500 hours in 2 years and it is great being up at someone else's expense!! In addition, if you get pleasure from seeing the light go on when a student finally understands what they're trying to do then you will find instructing very rewarding.
Just don't sell your soul to some unscrupulous club!!