I just bought an Osram T5 batten 28w and I thought it was instant start so I used 250v from the variac in hopes to heat the electrodes faster during starting. But it was programmed start so the electrodes glowed brightly white and the area near the electrodes was flashing abit like on switch start it was strange I tried few tubes it still worked in the same way. I hope I did not damage the circuit although it was pretty cheap hence I thought it was instant start.

Programmed start, provided the hot restart time is the same as the cold start. If turning on the lamp after turning off, starts the lamp within much shorter time or instantly, it is just a PTC based ballast, and not a real programmed start ballast.

I just bought an Osram T5 batten 28w and I thought it was instant start so I used 250v from the variac in hopes to heat the electrodes faster during starting.

On instant start ballasts the electrodes are heated up by the capacitor resonance current, which depend mainly on the voltage across the capacitor, so across the lamp. As the circuit operate in (rather high Q) resonator mode, the voltage depend mainly on the lamp glow discharge voltage, not on the mains input voltage. Consequently the same is valid for the heating current - does not depend on the mains voltage.

So increasing the ballast input voltage does not help, it may only cause troubles, mainly with the programmed start ballasts (even the simplest versions using the PTC):
The preheating current is way too high and as the filaments have shorter time constant than the PTC, it mean they would be overheating.
With the open loop frequency controlled designs it will cause higher voltage across the tube during the preheat, what could lead to premature ignition.
The most intelligent ballasts contain an overvoltage protection, what would cause the ballast to shut down, when the input voltage goes above the rated tolerance.

And if the ballast include an active PFC, it will not cause any difference, as the PFC (for "230V" mains ballasts) regulate it's DC output to about 400V regardless of the actual input. With marginally designed regulation loop frequency compensation it could cause the PFC to be unstable, causing high over- and mainly undershoots, with consequent erratic ballast behavior.

@dor: Even the simple PTC controlled ballast is qualified as a "programmed start", as with normal use cycles the PTC have enough time to cool down. The problems may arise only on motion sensors or similar simple controllers, what tend to cycle the lamp very frequently...

I tested the same light on normal mains (242v)and it did the same thing...both ends glowed brightly for 2s then the tube lighted. I cannot be sure if I had damaged the circuit or not unless I buy another one to test. As far as I know the PTC shouldn't be the culprit for overheating the electordes. The running of the tube is fine no blackening looks like new so I guess it's running the tube properly. Maybe it has a shorted resistor/cap in series with the PTC to reduce filament voltage.

The 250V can not damage the circuit.
And the overheating would not be caused by the PTC, but by the elevated (out of the specified range) supply voltage.
The 250V should not cause any troubles to the tube, but the lifetime optimum would be still at the rated 230..240V (but the difference would be very minimal).

I have ordered from the shop two T5 battens by Philips 14w and 28w both instant start I think I won't be using the variac this time after what happened. The variac idea worked very well with preheat CFL with glow bottle at the base set at 248v it eliminated sputtering during ignition and running so the tube ended up clean even after many hours of use. I may take a video of the set-up to show what I been doing.