According to Bloomberg's Mark Gurman the Pixel 5a will be announced in August. It will hit the shelves the same month.
For a context, the Pixel 4a was unveiled on August 3, 2020, and was released on August 20. It was available in the United States, United Kingdom, Australia, Canada, France, Germany, Ireland, Italy, Japan, Singapore, Spain, india and Taiwan.
Rumors also indicated that the Pixel 5a will not be a huge upgrade over the pixel 4a, mainly they want us to focus on the upcoming flagship Pixel 6 and Pixel 6 Pro, which are going to be this year's biggest and most interesting releases mostly because these two phones will feature huge design & camera sensor upgrade and definitely Google Silicon and probably it will be one of the best Android phones of 2021, expected in the last quarter of the year.
You can check out my The Alarm Talk show Ep on pixel 6 and 6 pro.