Two methods will delay the charging of a Powerwall:
Inject the dynamic pricing into the Powerwall and use Time Based Control mode, for example with NetZero. Netzero - Dynamic Electricity Pricing | netzero-labs
The other method is to use the TBC hack with a high export price in your utility rate plan, to set your Powerwall to export, then restrict exports to either solar only or never. So your Powerwall tries to export, but is limited.
The third method, which isn’t available yet is for Amber to provide API access to enable their Preserve mode.