If I understand you correctly, you probably want a timechart instead:
index=ndx sourcetype=srctp domain=* source="sourceurl"
| timechart span=1m dc(domain) as count by source
from User warren – Stack Overflow https://stackoverflow.com/questions/66110589/count-the-number-of-different-value-of-a-field-and-get-the-average-per-minute/66120697#66120697
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