turnerapadd said:

I asked support and found out that Resource Yielding boosts only work if you start them before sending troops to yield resources. What about other boosts - do construction and studying boosts affect current activity or are they only useful for the first minutes of activity?

So this boosts will work if you use it before the process start and if the boost ends during the construction or studying its effect will work  for the end of process

This is true of all boosts.

Even the game bonus on boosts has to be in effect before the boost itself is bonused. Thus if one of that day's bonuses is boost +10%, it does not take effect until you log out and in again. If it does not appear under Events / Assailants, Apostates, Bonuses, it is not in effect.

- things will expire as usual. Game's day cycle starts at 0 zulu. If a boost appears as above, at 0 zulu it will disappear. (Same reason assailants suddenly disappear. [The new ones appear 2h later.])

- so hit F5 refresh after 0z, daily. (UCT+0)

- don't start on an assailant or apostate on their last day near cycle refresh time. Nothing like being half way through an alpha and having it suddenly disappear on you!

Two interesting ramifications of this:

You can apply the boost, execute the action, and remove the boost. e.g. Training boost, start training, construction boost, start a building, studying boost, start a study, yielding and capacity boosts -send- a march out to yield. Put on training armor, start training, change armor, repeat.

Once on a screen where 'cost to upgrade' is shown (Building or Studying), the boosts are locked in. You can wait for resources to arrive to upgrade, and the boosts will still apply, even if the boost expires while on that screen. [So have all resources to hand before entering this screen. e.g. Click on rss at top, Apply whatever you need to, beforehand.] You can click on upgrade, get taken to the add resources screen, then back out, but you cannot back out further than that - or you loose any expired boosts.

- this includes things like capacity, speed, and yield boosts ... send the march out and the boosts apply throughout, even on the return trip. [Your Hero doesn't suddenly slow down when marching boost expires. It does on next trip.]

Simple concept: boosts must be in effect before action started - avoiding the complexity of mid-action boost expiry. Intricate ramifications though - like turning on a boost after the action has started ... and wasting the boost.

Been there, done that. Repeatedly ...

CORRECTION: GAME BUG - BOOSTS EXPIRE TRANSPARENTLY! Although nothing changes on the screen to let you know that. I have now experienced (and paid attention to) the time remaining increase (dramatically) before 'Upgrade' is clicked, and after. 

So ... keep an eye on the icons on the right ... counting down to when your boost will expire. If the icon changes, you may wish to exit the upgrade and reapply the boost.