The phrase "opening stretch" refers to the beginning part of something, like the start of a race or a project. It is the initial period or phase of an activity or endeavor. Full definition
As a result, more and more winter ice is growing on open stretches of water, making it thinner and more vulnerable to melting during its first summer. (newscientist.com)
It's got plenty to offer, from sweeping plains and vast open stretches to some of the country's biggest cities. (consolidate.loan)
It's summer — that wide - open stretch of time you've set aside to accomplish... everything. (gse.harvard.edu)