Well, you may consider factor timing under the ambit of Active management if you are placing active bets on various factors and individual securities together or you can take it to be under passive management if you are simply making factor bets without predicting the future moves of any individual securities.
Explanation: Factor timing as the name suggests is the art and science of timing the factors which affect your portfolio, there are loads of factors which may affect a portfolio. Say if you have a combined fixed Income and equity securities portfolio then some of the primary factors that would affect your portfolio would be-
1. Interest rate
2. creditworthiness of the portfolio securities
3. growth rate
5. currency movement
Now, that you have identified the factors that primarily affect your portfolio, you will have to understand them in relation to your portfolio and from an isolated perspective so that you may take a call on their direction of movement and the time frame associated with the movement.
There are single factor portfolio which allows for placing a bet on a single factor alone, in this portfolio the effects of all other factors are muted by using a long-short portfolio construction framework.
If you are using linear regression then you may play with the factors by manipulating the betas associated with those factors.