I recently participated in a couple of read-a-thons when knowing how much time I actually spent reading would have been useful. I wandered over to Amazon and searched. This is what I found: The Mark-My-Time digital bookmark.
This bookmark will either count up time or count down time. It is actually advertised as a way for kids (and parents) to keep track of time spent reading because research has shown that 20 minutes a day of reading time for kids has measurable benefits in school performance.
The Mark-My-Time bookmark comes in a variety of cool colors and is quite inexpensive. I paid $8.45. I chose hot pink for mine because sometimes I want to be a girly-girl. I recommend it for both reluctant readers and avid readers who want to know how much time they are really spending reading.