If you use tertile period you can add those periods in your custom timesheet.
How to implement custom periods
This is the periods for the 3 tertiles in the present year.
<period name="Tertile1TY">
<label locale="no">
<caption><![CDATA[Første tertial dette år]]></caption>
</label>
<label locale="en-gb">
<caption><![CDATA[First tertile This Year]]></caption>
</label>
<label locale="sv-SE">
<caption><![CDATA[Första tertiär i år]]></caption>
</label>
<label locale="nl-NL">
<caption><![CDATA[Eerste tertiel dit jaar]]></caption>
</label>
<label locale="da-DK">
<caption><![CDATA[Første tertiær i år]]></caption>
</label>
<label locale="de-DE">
<caption><![CDATA[Erstes Tertil dieses Jahr]]></caption>
</label>
<startDate><![CDATA[=Date({"mask":"CYmonthS", "offset": 1});]]></startDate>
<endDate><![CDATA[=Date({"mask":"CYmonthE", "offset": 4});]]></endDate>
<startTrendDate><![CDATA[=Date({"mask":"RyearS","offset":-1});]]></startTrendDate>
<endTrendDate><![CDATA[=Date({"mask":"RyearE","offset":-1,"output":"I","startofyear":"05-01"});]]></endTrendDate>
</period>
<period name="Tertile2TY">
<label locale="no">
<caption><![CDATA[Andre tertial dette år]]></caption>
</label>
<label locale="en-gb">
<caption><![CDATA[Second tertiary This Year]]></caption>
</label>
<label locale="sv-SE">
<caption><![CDATA[Andra tertiär i år]]></caption>
</label>
<label locale="nl-NL">
<caption><![CDATA[Tweede tertiaire dit jaar]]></caption>
</label>
<label locale="da-DK">
<caption><![CDATA[Andet tertiært i år]]></caption>
</label>
<label locale="de-DE">
<caption><![CDATA[Zweites Tertiär in diesem Jahr]]></caption>
</label>
<startDate><![CDATA[=Date({"mask":"CYmonthS", "offset": 5});]]></startDate>
<endDate><![CDATA[=Date({"mask":"CYmonthE", "offset": 8});]]></endDate>
<startTrendDate><![CDATA[=Date({"mask":"RyearS","offset":0,"output":"I","startofyear":"05-01"});]]></startTrendDate>
<endTrendDate><![CDATA[=Date({"mask":"RyearE","offset":-1,"output":"I","startofyear":"09-01"});]]></endTrendDate>
</period>
<period name="Tertile3TY">
<label locale="no">
<caption><![CDATA[Tredje tertiær i år]]></caption>
</label>
<label locale="en-gb">
<caption><![CDATA[Third tertiary this year]]></caption>
</label>
<label locale="sv-SE">
<caption><![CDATA[Tredje tertiär i år]]></caption>
</label>
<label locale="nl-NL">
<caption><![CDATA[Derde tertiair dit jaar]]></caption>
</label>
<label locale="da-DK">
<caption><![CDATA[Tredje tertiære i år]]></caption>
</label>
<label locale="de-DE">
<caption><![CDATA[Drittes Tertiär in diesem Jahr]]></caption>
</label>
<startDate><![CDATA[=Date({"mask":"CYmonthS", "offset": 9});]]></startDate>
<endDate><![CDATA[=Date({"mask":"CYmonthE", "offset": 12});]]></endDate>
<startTrendDate><![CDATA[=Date({"mask":"RyearS","offset":0,"output":"I","startofyear":"09-01"});]]></startTrendDate>
<endTrendDate><![CDATA[=Date({"mask":"RyearE","offset":-1});]]></endTrendDate>
</period>