I really liked this one! The graphics were a tad on the wonky side but give the time limit I think you're excused on that front.
I have three big recommendations if you wish to expand this:
1. better graphics, I assume we're in a birds eye view, so maybe show us what is inside the boxes so we can see that the light boxes are like, a few socks whereas the heavy ones are a fully computer with keyboard and mouse.
2. A weekly leaderboard! Just to incentivize people to keep pushing themselves
3. Perhaps the time limit could scale up whenever you drop a box in the goal spot, and a new box could appear throughout the stage every time you drop one in, so your end goal feels unachievable by design rather than by limitation.
Overall though, a really great game, the pick up mechanic is difficult due to accidental grabs, but it feels like it turns this into something of a rage game in some cool ways, so I wouldn't change a thing in that regard. Great work!