I've had these really vivid memories of this book but I read this around 2 decades ago so I might be completely misremembering things or mixing a couple books together.

I remember the protagonist, a child, receiving this box covered in vines. I think the vines grew through his bedroom and distorted his perception of time (not confident about this part).

I believe some tiny creatures (possibly invisible) came out of the box and started building a structure in the protagonist's basement. I think they were mostly harmless but got very aggressive when the structure was messed with by anyone. I remember the structure being finished and it was some kind of door to another dimension.

I think towards the end an adult who has experienced this before realizes what is happening and rushes to save the protagonist, and there was some kind of plot twist with the vines (probably the time manipulation).