If you have to ask you probably don't want to know but, see, there's this website called Beeminder which is a Quantified Self tool for the ironically hypermotivated to graph their progress on things like how they spend their time and also make really sure they actually make progress by literally agreeing to let Beeminder charge them when they don't. It's super motivating to certain lifehacking data nerd types.
And then there's this equally crazy tool, also by the folks beehind Beeminder, called TagTime which is really übernerds-only for now but the idea is you can randomly sample yourself to see where your time is going. (For many things RescueTime works beautifully and Beeminder has a nice normal-person-friendly RescueTime integration.) But for the doubly nerdy you can set up TagTime to automatically update a Beeminder graph and if you've done that you might find this tool useful.
The idea is that since TagTime randomly samples you, you can never be sure how much time you're going to get credit for. It works out exquisitely fairly in the long run but sometimes you have a beemergency and really need to get credit for another hour or so by midnight. So that's what this tool is for. It does the math on that (involving the CDF of a gamma distribution, as it turns out) to tell you how likely you are to get pinged (to use TagTime's lingo) enough times before midnight, if you stay focused. The best part is how it updates live so you can watch your chances dwindle away in real time if you're staring at this page instead of doing whatever it is you're beeminding and tagtiming.
You might also find this static table handy. It gives the number of hours you should set aside for the given number of Emergency Hours (Emergency Pings) if you want a 99% chance of getting that many pings.
|0h45m (1 eep ping)||3.5h|
|1h30m (2 eep pings)||5h|
|2h15m (3 eep pings)||6h|
|3h00m (4 eep pings)||7.5h|
|3h45m (5 eep pings)||9h|
|4h30m (6 eep pings)||10h|
|5h15m (7 eep pings)||11h|
|6h00m (8 eep pings)||12h|