You can combine the two like this:
earliest=-1h@h latest=-0h@h index=vha_pronto sourcetype=pronto_pil_logs ("pinless-product-offers" OR "siebel-order-details")
| eval class = case(searchmatch("pinless-product-offers"), "pinless", searchmatch("siebel-order-details"), "siebel", true(), "wtf")
| timechart span=5m count by class
This will search for both types of events, classify them [priority given to pinless here, in case an event contains both strings], and count each class of events over time, giving you two value columns / coloured lines in your chart.
Relying on just strings contained in your event is often okay, but I recommend using a field that contains the type of product offer you are looking for, and splitting the timechart by that field. Then you won't have to re-classify manually in every search. If you had such a field the search would look like this:
earliest=-1h@h latest=-0h@h index=vha_pronto sourcetype=pronto_pil_logs (product_category="pinless-product-offers" OR product_category="siebel-order-details")
| timechart span=5m count by product_category
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