Thiruvaradhanam should be done during the third part of daytime; that is, after abhigamana and upAdAna kAlam. The daytime period between morning 6 am and evening 6 pm is divided into five parts and thiruvaradhanam should be performed during the third part called Ijya.
If thiruvaradhanam could not be done during Ijya kalam, it can be done before ijya and if that is still not possible, it can be performed in the evening.
But one should not perform it regularly in the evenings; it is allowed only as an exception when one could not do morning thiruvaradhanam due to unavoidable circumstances.