If
P = Probability of spending money (as a fraction)

Then P is directly proportional to t, as denoted
P α t

As t approaches 24, P approaches 1
Or, as t → 24, P → 1

Demonstrated by the equation:
P = (1/24)t
or
P = t/24

For example, if I spent 1 hour on the internet yesterday (t  = 1)
P = 1/24

Roughly speaking, that translates as if I went on 24 shopping websites, I would have made a purchase from 1 of them.

If I spend 4 hours on the internet today (t = 4)
P = 4/24
Therefore P = 1/6

Which means I will buy something from a sixth of all of the shopping websites I visit.

As proof, I offer you this:

Today's History
Waterstones.com
hmv.com
play.com
etsy.com
xkcd.com store
ebay.com

Today I bought 5 books ebay.

Q.E.D.

The scary part is, this equation is trufax. I'm gonna be so poor if I don't reduce t.