The phrase "at first usage" is correct and usable in written English.
It can be used to refer to the initial instance or occasion when something is used or applied.
Example: "At first usage, the software seemed complicated, but I quickly learned its features."
Alternatives: "upon initial use" or "during first application".
Panel B downloads the applet once clicked (only at the first usage) and loads up the XML data to visualize the pathway.
Allemagne admits to shedding a tear at the spray's first usage last summer.
He said that at first, however, usage would probably be limited to the patients who are not eligible for Avastin because of the risk of side effects from the Genentech drug.
At first I could see that the subsequent usages were adjacent to the first party of the first usage.
After Augustus, the road gave its name to the district which formed the eighth region of Italy (previously known as Gallia or Provincia Ariminum), at first in popular usage (as in Martial), but in official language as early as the 2nd century; it is still in use (see Emilia).
At first impression, codon usage does not appear to have reached an equilibrium in Populus as there was an excess of U → P substitutions across the entire phylogeny (Table 2).
At first, almost all usages were hyphenated, as in fancy-shmancy; this gave a singsong effect, however, which did not reflect the shrug of studied indifference implicit in the phrase's meaning.
Personally, I find the second usage more irksome.
The second usage level aspect is the overall look of the scenario flowchart (e.g., basic usage level flowcharts [or flowchart steps] are easier to understand for non-programmers than flowcharts at the advanced or ultimate usage level).
At the Coleman trial, Leonard noted that many of the killer's spray-painted sentences began with the word "fuck," as did the e-mails and letters — usage that at first might seem common.
