Unlike amals there is no specific time for doing an Isteqhara. They can be done at any time that suits us. Some people have a misconception that Isteqhara should be done only at night or after Isha namaz. However, this is not the case. They can be done at any time. The only condition for doing an Isteqhara is that it should be done with full concentration so that we can get the instructions or guidance from Allah successfully.