Idea of the reactor is to maintain levels, not really to bring them up from the bottom. Since your levels are near ideal, get it going now and monitor.
You still can tweak your levels a bit by the following:
Measure and record alkalinity every few days and compare the readings. If the alkalinity level is falling, increase the amount of CO2 so more of the medium is dissolved. Conversely, if the alkalinity level is rising above the level you want, reduce the amount of CO2 so less of the medium is dissolved.
The bold was cut from this
article a really nice piece about Ca reactors.