You can restart a previously used duration from History and pin frequently used durations as favorites at the top.

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Tap Unit in the upper-right corner, then select History as the time unit.

Tap the duration you want to use in History to start a timer with the same duration.

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Tap the ☆ to the left of a History item to pin it to the top as a favorite.

Touch and hold a favorite at the top, then drag it to change the order.

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The free version lets you set one favorite.

ListTimer Plus lets you set multiple favorites.