[MarketPress eCommerce] change the sale price field from date to date-time

Hello,
(first, my english isn't the best, sorry)

i'll change the field "sale price" from date to date-time format.
Width that i can make offers for a time slot like: sale price from 12:00 to 14:00 a clock.

How can i change the sale price filed to this format?
And make that change any problems width the rest of the plugin?

Thank's and best regards