At room temperature, mine takes about 3-4 minutes heating until the lamp will start. You'll see RbMon showing SD2 and AD4 at max values, then they'll settle back into something sensible once it lights up. After that, you're watching the DS signal values and hoping the (large, small) turns into (small, large). 
Mine had a blown capacitor in the lamp circuit, thus it wouldn't ignite; SD2 and AD4 never budged. I opened it up to find a cracked tantalum cap: http://imgur.com/bASgB After replacing the cap, I now get lamp ignition but it doesn't achieve lock. (Photocell signal AD9 very low.) Once I swear I saw RbMon claim it had locked, about 6 minutes after power-up, but a moment later it was back to unlocked state and it's never repeated that feat. No idea what happened there.
I'm wondering whether one can simply use it as a nice (albeit power-hungry) OCXO. If given 1pps from GPS, will the quartz discipline itself even without the Rb loop running? 
-Nate B-
Stephen Tompsett (G8LYB)  wrote:
>                 Use the RbMon utility to monitor the unit's operation as it starts up to
> confirm that the lamp is started and the photocell is detecting a signal.
> Not long ago there were a number of units available for sale on Ebay
> that appeared to have a lamp problem.
> 
> On 23/08/2013 02:10, Paul wrote:
> > As I patiently wait for my PRS10 to lock I'm curious if there's a
> > limit beyond which I should assume the unit is faulty.
> >
> > It does produce abount 10MHz (+- .2 Hz) and the oven current dropped
> > at what I assume is operating temperature.
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> --
> Stephen Tompsett (G8LYB)
> 
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