Use a CD4536 oscillator/frequency-divider/monostable.
Use a reasonable oscillator frequency then set it to divide it up to 2 to the 24th power (you work it out) for a 48 hours output.
Set its monostable to 5 seconds and for it to be triggered by the 48 hours output.
Can you give me a little more details than that. Most likely I'll be buying a bread board and soldering jumpers between chips but I don't know how to do it. Possible Schematic?