Cycling the QT well and using hypo or copper is the slower but easier and less work intensive method than TT. Basically the former should last at least 8 weeks.
When you leave behind the issue of ultimate effectiveness and the issue of increased chance of bacterial infection, such is the feature of each method.
The cycle QT method also get rid of most ick quickly. There is reason to believe that it is faster in symtom relief than TT, which uses no drug. Some state that copper has no effective on ich already on fish, but I think this is not true.
Since you have to take the vacation, the only choice is between leaving fish in QT that is not cycled (even with the doubtfully half cycled rock) and returning them to DT earlier than ideal.
From what I gather, I believe returning them to the DT in less time (7 weeks) then most desirable is better than leaving them in uncycled QT. The chance of ammonia harm is greater than the risk of ick.
As I have said, even if ick returns, there is also a very good chance that ich infestation will not yet be serious enough to kill your fish within two weeks of the fish in DT.
You should plan to have to treat your fish at once when you come back. For this reason, you should start a cycle now in a separate container.
Read the thread "another lesson learned" closeby. There, I outlined the procedure to start a cycle with good circulation, aeration, warmth, bacteria seed, and pulses of ammonia.
The pulses of ammonia can be shrimp blended into milk, or at least very finely chopped. Use a small shrimp for each 20 gals of water. Forget about removing any shrimp, let what you put in decay entirely. (use a fraction of a small shrimp for less than 20 gals of water) . Add one pulse at day 1, and every five days twice. Three pulses for the cycle. If you are leaving soon, double pulse on the day you leave.
If ich had broken out when you return, you can use TT and in one to two more weeks the cycle will be advanced to the point that the medium can be used in QT, after rinsing with clean salt water of the same salinity.
If ich broken out later when the cycle is complete, you can choice to give up on the TT method and use the slower method to eradicate ich.