doodle.com is a well known page for scheduling meetings or making decisions. Its calendar integration is probably less known. Doodle can export a calendar with the dates you have chosen in order to remind you to keep them blocked. When a date is fixed for a query, doodle releases the other dates. You can also add your calendar to doodle to see your availabilities right in the doodle calendar and to use such features as autofill.

If you look for something else, calendly.com is another free service that provides an interface for others to schedule a meeting with you. Dates with concurring events in your Google calendar are automatically blanked out.