Presumably this has already been resolved,
However from the tenants perspective, this could possibly be from them misunderstanding the safety measures openrent provides. It’s likely they have delayed payment in this manner as a way to make them feel more secure about them paying until they have something tangible.
In this case, I would just highlight how Openrent secures it for them and that you do not actually handle the deposit and first month’s rent for this reason.
It however could be that they understand this but perhaps do not have the cash flow before their own deposit is paid back from their previous rent - did you try asking them for their situation?
I agree in your shoes it’s a big ask as if they are unable to pay, you have lost out time to market the property and a month’s rent - however I think its always important in these tentant landlord relationships that there is some element of trust from both parties - you are after-all embarking on what is essentially a partnership together and it always helps for both parties to be in sync and on the same side.