eeprom erasing time???
Bright direct sunlight can gradually erase an EPROM (that's mentioned in the AMD data sheet), but it could take weeks depending on your weather and latitude.
Back in the days when I used EPROMs, I would test a new unknown UV lamp by checking the EPROM periodically to see when it appeared blank, and then I'd give it an additional dose of twice that time, just to be sure. For example, if it appeared blank after 15 minutes, I'd give it an additional 30 minutes for a total of 45 minutes.