The phrase "a day to complete" is correct and usable in written English.
It can be used to indicate the amount of time required to finish a task or project.
Example: "The project is due next week, and we have a day to complete the final report."
Alternatives: "one day to finish" or "24 hours to complete".
It was only at round two, a form that took most of a day to complete, that she started to take the prospect seriously.
The overlapping exposures of his panorama took him a day to complete; laid end to end, they flatten the circular view into a strip that measures more than 17 feet.
In contrast, electronic payments between bank accounts, even within the same country, can often take more than a day to complete.
Each day's content takes about 5-15 minutes a day to complete and includes writing prompts (a key part of many CBT programs), breathing exercises, and audio recordings.
WASP-18b and its star are so close to each other that it takes the planet, which is described in tomorrow's issue of Nature, less than a day to complete a revolution.
The designers have $100 and a day to complete their looks.
WASP-12 circles so close to its sun it takes only a little more than an Earth day to complete one orbit that its surface temperature exceeds 1500°C, making it the hottest alien world ever found.
Portaledges, he explained, are used by mountaineers to sleep on during vertical wall ascents that would take more than a single day to complete.
Patients who were clearly taking action developed conscious strategies to overcome these constraints, such as choosing a set day to complete their modules, or using the date of the face-to-face consultation with the therapist as a deadline.
Tiger Woods won a record seventh title here in 2013 when fog wiped out the third round and necessitated an extra day to complete the tournament.
It's about a character who has one more day to complete his/her Phd dissertation (or some other academicy paper).
