The time cannot be predicted. The keys cannot be released to you until the closing has taken place unless alternative arrangements have been negotiated beforehand.
Most typically it will be mid to late afternoon and before 5:00 p.m. But speak to your REALTOR® or attorney, he will let you know and keep you updated as to when the transaction is expected to close.
The sale of the severed portion of vacant land would not be subject to GST/HST since it is not capital property used primarily (more than 50%) in a business and it is not being sold in the course of a business. However, if the land was subdivided into more than two parts, sales of the severed portions are not exempt unless the portion is sold to a relative (or to a former spouse or common-law partner) for their personal use.