Errr..you're not making it easy for yourself! Measuring this in a school / college lab would be easy (if they've got the right equipment, which they should have), you would feed the connections into a piece of equipment called a counter/timer and it would just time the delay for you. You can (as Ken said) build such an instrument reasonably easily from scratch if you know something about electronics and/or have someone around to guide you, but it doesn't read like that will be the case. Much easier (although more expensive) would be to use a PC interface like "Analog Discovery" or "PicoScope" (each around £150, rather less if you're lucky): you connect each of your break wires to its own resistor (value doesn't matter too much, but about 1kOhm would be about right) and then to a battery, and connect each of two channels of the PC interface to one of the two wires. I expect if you do a web search on using a PicoScope / Analog Discovery as a timer you'll find examples.
Bigger problems, having thought about this over the weekend:
a) how are you going to emdeb the wires in the glass (since it needs to fall freely)?
b) isn't the act of embedding the wires going to affect the stresses within the glass?
If the wire's thin enough I guess it may work with the wires attached (superglued?) to the outside of the glass?
Andy Millar CEng MIET CMgr MCMIhttp://www.linkedin.com/in/millarandy
"The aim of argument, or of discussion, should not be victory, but progress." Joseph Joubert