The word rendered here as "redeeming," means "to purchase; to buy up" from the possession or power of anyone; and then to redeem, to set free-as from service or bondage. Here it means, to rescue or recover our time from waste; to improve it for great and important purposes.
 

They redeem their time who employ it:

(1) in gaining useful knowledge;

(2) in doing good to others;

(3) in employing it for the purpose of an honest livelihood for themselves and families;

(4) in prayer and self-examination to make the heart better;

(5) in seeking salvation, and in endeavoring to do the will of God. They are to redeem time from all that would waste and destroy it-like recovering marshes and fens to make them rich meadows and vineyards. There is time enough wasted by each sinner to secure the salvation of the soul; time enough wasted to do all that is needful to be done to spread religion around the world, and to save the race. We should still endeavor to redeem our time for the same reasons which are suggested by the apostle-because the days are evil.

There are evil influences abroad; allurements and vices that would waste time, and from which we should endeavor to rescue it. There are evil influences tending to waste time:
 

(1) in the allurements to pleasure and amusement in every place, and especially in cities;

(2) in the temptations to novel-reading [or watching TV], consuming the precious hours of probation to no valuable purpose;

(3) in the temptations of ambition, most of the time spent for which is wholly thrown away, for few gain the prize, and when gained, it is all a bauble, not worth the effort;

(4) in dissipation-for who can estimate the amount of valuable time that is worse than thrown away in the places of revelry and dissipation;

(5) in wild and visionary plans-temptations to which abound in all lands, and pre-eminently in our own;
(6) and in luxurious indulgence-in dressing, and eating, and drinking.  ~ Barnes
 

Buying up those moments which others seem to throw away; steadily improving every present moment, that ye may, in some measure, regain the time ye have lost. Let time be your chief commodity; deal in that alone; buy it all up, and use every portion of it yourselves. Time is that on which eternity depends; in time ye are to get a preparation for the kingdom of God; if you get not this in time your ruin is inevitable; therefore, buy up the time. ~ Clarke

Note:  In Ecclesiastes we read "...time and chance happeneth to them all. For man also knoweth not his time (Eccl 9, last part of verse 11 and first part of verse 12)."  The word "chance" means "opportunity"...time and opportunity happens to all humans. The word "time" actually means "death."  Therefore it should read, "death and opportunity happens to us all."  We do not know how much time we have.  We do know that time is the ONLY real commodity we have.  Time is what gives us opportunity.  Like a financial budget, we can allot our money for wise purchases or for foolish purchases.  After writing out the budget, our job and duty is to go over it and identify the foolish items in the budget.  When we have identified them, we can allot that "rescued" money and put it to something wise.  In doing so, we have redeemed some money.  It is the same with our time.

Our time is much more precious than our money.  There may be no limits on how much money one could earn, but each individual has only so much time and even lesser time from his or her calling into the Salvation Process until death or the return of Jesus Christ.  The Barnes commentary above gives us a sample list of the wise and foolish purchases with our time.  God wants us to address, at every opportunity, the elements of the Salvation Process:  Bible study, prayer, meditation, overcoming sin, and invoking the Holy Spirit in the form of Godly principles--living the gospel.  He wants us fully immersed into His Word.  This takes time.  We redeem the time by taking minutes and hours from the foolish side of the ledger and applying them to the wise side of the ledger, actively and diligently working the Salvation Process.