There are a number of synonyms for the phrase "this evening," including "tonight," "later on," "afterward," "at nightfall," "at dusk," "when the sun sets," and "in the evening hours." These phrases all convey a sense of time later in the day when the sky darkens and people tend to relax after a long day of work or other activities. Depending on the context, different phrases may be more appropriate - for example, "tonight" may be more casual and conversational, while "in the evening hours" may be more formal and precise. Whatever the phrase used, it's important to communicate clearly and concisely to avoid any confusion or miscommunication.