One of the reasons is that I've seen it as a common practice with other software I used. For instance, the demo version of Traktor Pro 2 DJ-ing software closes itself after 30 minutes.

We've also set a high quality bar for us with 30 minutes. If the product doesn't deliver on its promise in 30 minutes then it means we need to do better.

We chose the 30 minutes instead of making the product a 7-day or 14-day or 30-day trial because we prefer freemium to software trials. With a number of days for you to try the software you can for instance install on day 1, go to a business trip on day 2 and when you return on day 7 realize that the software expired and you didn't even get the chance to try it out. With the attention economy of today, we believe day-based software trials are broken.

With Boxifier, if you don't find the time today you can try out the premium features again tomorrow, next week or whenever you find some free time because the product never expires.

to promote open source spirit...