I was digging through about this recently to suss a new budget scaling strategy and I don't have a source but I recall reading 15% or preferably less per day. I use rules and scripts for things like this. I have a rule that increases the budget a little every day as long as the CPA for the campaign is below my upper limit. It's more of a slow, controlled scale that way. I run on past 7 days data to smooth out weekly trends and anomalies and at 11pm so that the data is mature enough that most conversions have been processed and attributed. And yes, I have an identical but opposite rule to scale it back if it's gone too far.