You cannot control the timer directly from another panel, but you can create a button in your timer panel that turns it on/off, and trigger that button from another panel.
1. Make a button in your timer panels that turns on the timer. Give that button a TiggerID. You can also make that button invisible if you prefer to not have it onscreen, by adding "visible=false" in its definition.

In your other panel, create a button, and use the "Fire GPI" visual logic block, like this:

That should trigger your other button. Here are the 2 panels I used to test this out.
Timer Panel (with no actual timer, just an invisible button that would turn on a hypothetical timer. That button prints "ON" in the debug console when triggered)
<abs contexttype="opengear" id="_top" keepalive="false">
<button buttontype="push" gpi="TIMERON" height="62" left="101" name="Turn On" top="56" visible="false" width="144">
<task tasktype="ogscript">
/*! block id=1000 !*/
ogscript.debug("ON");
/*!!
<block id="1000" type="ogscript_debug" x="10" y="100" w="243" MESSAGE="ON" />
!!*/
/*!!<checksum>a1d91dcf454f56f916ac0898484ba7da</checksum>!!*/</task>
</button>
</abs>
Other Panel:
<abs contexttype="opengear" id="_top" keepalive="false">
<button buttontype="push" height="96" left="162" name="remote on" top="190" width="223">
<task tasktype="ogscript">
/*! block id=1001 !*/
ogscript.fireGPI("TIMERON", "", true);
/*!!
<block id="1001" type="ogscript_gpio" x="10" y="100" w="243" GPI="TIMERON" STATE="" GLOBAL="true" />
!!*/
/*!!<checksum>0b55b984ba449a36f92d0750bc1411b8</checksum>!!*/</task>
</button>
</abs>
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