now or later?

The terpenes only influence the high a bit, harvesting at the right time will do wonders, you can't get a fully sativa high from a indica but you can't get a fully indica high from a sativa, what you can do is make a indica feel hybrid by harvesting with clear+cloudy trichs being that the majority of trichs will be cloudy, just like you can make a sativa be traced with indica type high by letting her go full ambar. In this case white widow is a pretty well balanced high and the influence will come from the trichs, harvest as soon as up to 5% of trichomes are turning ambar and don't let it go any further than that and you will get the classic energetic and active but relaxed white widow high.

Trying to get a sativa high from an indica plant is like trying to get oranges out of an apple tree. If you want a sativa high, grow a sativa plant. Try looking for 100% sativa photoperiod plants, they are hard to find, but they do exist, I've grown High level, which has a great energetic high.