Time machines provide a fun learning experience, a unique business opportunity, and a contrived way to manipulate your plot arc. Watch out, though — depending on the make and model you choose for your temporal vehicle, they can often be expensive to build and difficult to maintain. See below for several types of time machine, along with assembly instructions when available.
The mechanism for how a hot tub can become a time machine isn't well-explained. However, if you acquire a hot tub and the chronological mechanism never works, at least you have a hot tub, right? For further instructions view:
Hot tub time machine [videodisc] by Metro-Goldwyn-Mayer Pictures and United Artists present a New Crime production
If you're willing to brave Bed Bath & Beyond's 'Beyond' section and don't already have enough remote controls, a pre-built time machine may be as easy as a trip to the store: