Prime Time NTP

Version 1.2: the complete four-timestamp NTP exchange, a filter that picks the best measurement rather than the newest, and timing that knows Wi-Fi from cellular.

"Prime Time" is a high-precision time app that shows the true time, accurate to the millisecond.

It queries multiple NTP servers directly — the same infrastructure that keeps the internet in sync — and works out the correct time from their answers. Your device's own clock is never used for the display.

[New in version 1.2] • The complete four-timestamp NTP exchange. The time a server spends preparing its reply is now removed from the measured delay instead of being counted as network transit. • A clock filter. Each server keeps its last eight exchanges, and the one with the lowest synchronization distance is used — not simply the newest — so one congested query no longer drags the reading with it. • Best-source marking. A green double ring shows the server with the lowest estimated error. The device offset is measured from that server and quoted with its ± accuracy. • Wi-Fi and cellular awareness. The link in use is shown, and an optional warm-up avoids measuring a radio that has just woken from idle. • Two in-app help screens explaining every mark on the display, and the reasoning behind how often servers are queried. • Japanese interface when the device language is Japanese.

[Free] • Real-time sync with up to 5 NTP servers • Millisecond display, refreshed up to 120 times a second on ProMotion screens • Offset and round-trip time per server, with sparkline history • Stratum and reference clock ID per server • Adaptive polling that eases off as a server proves steady

[Pro — one-time purchase, no subscription] • Manual sync on demand • Keep the screen awake while the app is open • Up to 30 NTP servers monitored at once

A note on accuracy: a round trip is a single number covering two unknown halves, and nothing in the exchange reveals how it was divided. Prime Time widens the reported ± rather than inventing a correction to hide it. On cellular, where the two directions are least alike, that margin is wider — and shown.

Made for developers, network engineers, and anyone curious about how far off their device's clock really is.