Well yes, it's possible seeing as the Daleks are basically going into the fight with both their appendages tied behind their backs. Could the Gunbuster take planet-buster weapons? How fast are the shots that it fires?Given that the firepower of Super Exelion era Gunbuster is less "destroy a planet on purpose" and more "destroy a gas giant that happened to be somewhere near what you were shooting at" the Daleks can be stopped in this scenario.
This is highly dependant on what time travel is allowed. The OP mentioned that "minor" time/relativity weapons/effects are permitted, but we need some context. Especially as pretty much anything short of "total universal destruction" is minor to a Dalek. What does "minor" temporal/reality powers mean in this scenario? What is a "minor" temporal disruption that would be permitted?Gunbuster Earth is one of the real high power 'verses, the kind that you don't fuck with unless you have strategic weaponised time travel (which is disallowed in this scenario).
For example, could the Daleks use the time-vortex to travel from one place to another (provided they remain in the same relative time period as everyone else)? If so, this would allow them virtually instantaneous travel anywhere in the area. Could they do things like slow ships down/ speed them up? Freeze ships/weapons in time? Generate paradoxes? Could they emergency temporal shift? Could they shift themselves 1 second ahead of the rest of the group and pretty much disappear? Again, all minor stuff from a Dalek's point of view.
Perhaps to make things more fair (and not have a shitload of ships get blown up right off the bat) we could add a couple more restrictions. For example, the Dalek Saucer could be the crippled one from "Victory of the Daleks" with only the few Daleks on board plus the Progenator Device. And the Dalek Emperor ship could be from immediately after the Time War ends, with the ship heavily damaged and the Emperor as sole survivor. In that scenario even the Daleks would know that they couldn't hope to win via brute force, and they would have to play things out very carefully instead.