foundry/Data/systems/pf2e/templates/items/partials/duration.hbs

<div class="form-fields">
    {{#if (or (eq duration.unit "unlimited") (eq duration.unit "encounter"))}}
        <input type="hidden" name="{{base}}.value" value="-1" data-dtype="Number" />
    {{else}}
        <input type="number" name="{{base}}.value" class="left-of-select" value="{{duration.value}}" />
    {{/if}}
    <select name="{{base}}.unit">
        {{#select duration.unit}}
            {{#each units as |label key|}}
                <option value="{{key}}">{{localize label}}</option>
            {{/each}}
        {{/select}}
    </select>
</div>