Yes, you need a timer for the dosing pumps. The time you have them run is all dependant on your tank. Use the BRS calculator.
http://www.bulkreefsupply.com/reef-calculator
To use it, you test your alk and calcium levels. Then input them and what you want your tank to be at and it tells you how much to dose approx. Once you get your tank up to the levels that you want, let it sit for say 3 days without dosing at all. Test the parameters again and see how much each one has dropped. Plug those values back into the calculator and divide by the 3 days and it will tell you roughly how much you need to dose of each every day. Bump your perameters up by the amount it tells you to dose, once you are good again, then start running your timers based on those daily values. As an example if it tells you to dose 30ml of calcium a day, the dosing pump you get has a rate of 1.1 ml per minute so 30/1.1 = 27 minutes of total dosing.
Spread everything out. Generally, you want ALK dosing during lights out because it does increase your ph levels. Your ph levels will all ways be lower during lights out so that is the best time. Calcium can be dosed at any time. Mag can be does up to 100ppm a day. You don't really need a dosing pump for mag as it can be done easily by hand to top off your levels.
Be careful not to increase alk more than 1dkh per day as it can stress your tank. You will still need to test quite a bit at the start and adjust your timers up or down until you find the general sweet spot of your tank. As your SPS grow, you will have to increase your dosing time to compensate.
It may sound complicated but it is actually really easy to do. Just be prepared to do a lot of testing at the start until your dosing pumps are set properly. If you find your levels a little low at the end of each month, then just manually add some more to bump up your values. Then add a few minutes to your timer. If you find them high, then lower by a couple minutes on your timer.
On my 180G, I only need to run my cal for an hour a day and my alk is about 40 minutes each day. Most of my SPS are all frags though. Once they grow considerably, I will be dosing a lot longer than that.