It varies on factors outside the universe as we know it.
Though within the universe time tapers... always and forever, sometime parallel to material aging and sometimes polar to it, though time being merely an observable variable, this appears to mean more than it does... Psychological grasp of the motion of time amounts to little more than a novelty, actual real world alterations in temporal shift, alter only the subject, not the entirety of the area around such a thing.
Reversing temporal fields amount to measurable factors across other dimensional qualities. Again, as with zero point, we can see it, protect against it, but not truly insert a probe to accurately produce usable results, only intriguing results.
We can use time without pondering that issue in all ways, we will in fact do so, though no real endeavor to toy with it will be needed.
Unless usable results to you are to reach your own grasp that this is true and have a few novel tools for localised alteration faster. Though it begs the question why send extremes, IE: a bomb or some fruit, forward in time?.. The field will be affected by altered environmental factors too... That we have too much fruit today and not enough tomorrow is best fixed using resources wisely, not emitting vasts amount of energy to achieve the same result.
To localise temporal alteration the other direction alters everything, even in the facility, unless off world.... Temporal linearity of harvesting is flawed unless some other you dies because of it in another dimension. And that is simply non-viable in any terms applied as paradox occurs, paradox at %>0 error margin in one form or another which would not be realised, thus some form of decay would occur, if universal linearity of physics is standard, the decay margin variances set in taper as they are, allowed for in equations.
Forever we expend vast amounts of effort in placing tomorrows harvest from area one in area two's box, when errors we cannot account for need only be patiently averted, with patience and planning..
To step into temporal sciences use of time itself, we would have to prove our worth to alien races who fear their destruction. In my opinion, for little more than a novelty of expedience, in a universe where eternal survival already exists.