"at daytime" is correct and usable in written English.
You can use it to refer to the time of day when it isn't night. For example, "I always love to go for a walk at daytime."
With this plan, the London-based venue plans to develop unused space and bring in more activity at daytime.
But being on antidepressants, if you're not careful you can just be sitting on the couch looking at daytime TV, eating and doing nothing at all".
It is tempting to see these pictures (one at daytime, the other night) as a reflection of the artist's lighter and darker moods.
The geomagnetic storm occurred at daytime locally.
We human work hard in fields at daytime.
The underestimation is more evident at daytime than at nighttime.
In particular, the solar radiation is available only at daytime.
The overestimation is more evident at daytime than at nighttime.
The RSI is operating at daytime while ISUAL is active at night-time.
The average humidity was 31% at daytime and 36% at night.
The underestimation is more apparent at daytime than nighttime, particularly during the noon bite-outs.
