Cascading timers
Six timers with presets of 28800 seconds each. If you are using a PLC processor with a numerical limit of 32767 then that limit gives you a little over 9 hours for a single timer running and using a 1.0 second time base. So, using six with the preset above will require the cascading. Cascading is just when one timer finishes and is done, then that done bit is used to start the next timer and so on until you have the entire process complete. You can reset the whole thing by using the done bit to turn off the first timer in the sequence and that in turn will drop all the others. There may be other ways but this will work. One caution, timing this long makes room for error so if you need really precise 48 hour time markers, then there may be a better approach than this using a PC or some other non-plc device that you can use to signal the PLC to do its work. Good luck!