Prepositions of Time and Duration in Technical English

Since is correct. Use since with a point in time (a specific moment when the action started): a date, month, year, or named event. "Since March" = starting from March up to now. This requires the present perfect or present perfect continuous: "has been working since March." Contrast with for: use for with a duration (a period of time): "for three months", "for two sprints", "for six hours." Memory rule: since + point, for + period. Common tech errors: "We have this bug for weeks" → should be "for weeks" with present perfect; "Since a long time" → incorrect, use "for a long time."

By is correct for deadlines. By + time expression means "no later than" — the action must be completed at or before that point: "by the end of Q2", "by Friday 5pm", "by the next sprint." This is the standard deadline preposition in project management English: "The feature must be shipped by release day." · "All tests must pass by merge time." Contrast with until: until means the action continues up to that point, not that it must complete by it: "The server will be in maintenance until midnight" (continuous until midnight). Never use since or during for deadlines. For expresses duration, not a deadline point.

During is correct. Use during when something happens at some point within or throughout a named period or event: "during the failover window", "during the deployment", "during the maintenance period." During answers the question "when?" by referring to a named interval. Contrast with for, which gives a measured duration: "for 45 minutes". You can often use both about the same event: "The service was degraded during the migration" (named event) vs "The service was degraded for 20 minutes" (measured time). In incident reports, during is used with named events (failover, deployment, outage window) while for is used with measured durations (for 3 hours, for 2 minutes).

Since is correct. Since + a named event or point in time marks the starting point of an ongoing situation that continues to the present: "since version 2.3 was released" = from that release up to now. This requires present perfect: "has been misconfigured since." Tech examples: "This bug has existed since the refactor." · "Performance has degraded since the last deployment." · "We've had this issue since the database upgrade." Common trap: mixing since and for. Ask yourself: is it a point (→ since) or a period (→ for)? "Since the release" (point — the moment of release). "For three releases" (period — across multiple releases).

For is correct. For + duration expresses how long something lasts or should last: "for 24 hours", "for 7 days", "for the duration of the session." In technical specifications, for is used to set retention periods, timeouts, TTLs, and SLA windows: "Data must be retained for 90 days." · "Tokens expire for 1 hour." · "The connection timeout is set for 30 seconds." Contrast: "The cache has been set since deployment" (since = starting point). "The cache must be updated by midnight" (by = deadline). "The cache was cleared during maintenance" (during = within a named event). Summary: for = measured duration, since = starting point, by = deadline, during = within a named period.