I also suffer from a rather short attention span (as many people will testify too). I'd get my G code all ready, get it loaded into Repetier and manually turn on the bed and extruder. Invariably I'd get bored waiting and would wander off and get distracted doing something else, only to return 20 mins later to a pool of PLA that had dripped from the extruder.
I'd been looking at various G-Codes and noticed that there is a code that waits for the bed to reach a target temperature.
The M190 command will wait for the bed to get to your target temperature, while M109 will wait for the extruder to get to the target temperature.
With this, I added the following to the Printer Settings/Custom G-code in Slic3r:
M190 S[first_layer_bed_temperature];The first command will turn on the heated bed and wait for it to get to the first layer temperature you've set, while the second command just starts the extruder heating. I then home X & Y and when that's done I wait for the extruder to reach the first layer temperature with the fourth command.
G28 X0 Y0;
Now I just hit 'Run' and the printer will do the rest. No more drippy PLA for me!
Note: You can swap the order of the M104 & M190 commands, the extruder will start to heat up and then the printer will wait on the bed to heat up. This will reduce the time spent waiting, but you will also have the extruder at temp for most of the time the bed is heating up. This will probably reduce the amount of PLA in the extruder once the print starts. Just something to be aware off.