It is depended on services, but normally eVoucher is valid for 60 days after purchased date. Please check term and condition before purchase.

Book a service for multiple people:
    Bookings for multiple persons are not available at this time; you will need to book for one person at a time. If you book for several people, you can write in the comment box about the previous bookings so the partner is informed and aware about several bookings 

Buy multiple Vouchers/coupons:
    You can increase a quality at checkout page, but it’s only available GoWabi application.