It happens that because your two time ranges are adjacent, you could do something simpler, though it's only marginally so. And it less efficient if the time ranges have a large gap between them:
index=summary source=dailysearch OR source=hourlysearch earliest=-7d@d latest=now
| stats count(eval(source=="dailysearch")) as dailysum
count(eval(source=="hourlysearch")) as hourlysum
However, I would also note that it's a good idea to store different densities of summary (e.g. daily vs hourly) into different indexes, because you'd then be able to archive/delete, e.g., all the hourlies after one month, while keeping all the dailies for two years, and save on disk space.
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