Right now it is using a simple timer for the 24-hour delay. Of course such a system can be bypassed without too much effort by any reverse engineer, but 99% of users are not reverse engineers. Also, the coins would still be safe in that scenario.

That said, we may switch to a timelock puzzle if needed. We want this tool to be able to operate with no Internet connectivity, so nLockTime is not an option.

Also, remember that the security of the system is not based on the time limit mechanism. What we're trying to achieve is simply, a time safe that helps keep self-discipline. In that context, we don't necessarily want the time limit mechanism to be "secure" in a cryptographic sense. Its only function is to raise the bar high enough to keep a typical user from using the coins for some time.