Your HSA provider should have some better options. Typically, you put the money into the HSA and then from there you can invest a portion of it like it was an IRA. They often require you to maintain some cash balance (mine is $2,000 for example) before you can invest the additional money.
If you have good investment options in the HSA, then you should deposit it in as early as possible and let it grow, NOT using the HSA to pay for medical expenses if you can afford to pay it out of pocket outside of the HSA. Keep your receipts.
You can use those receipts to reimburse yourself at any point in the future when you need that money.
Also, if you can make your contributions come from a payroll deduction, you also get to avoid paying FICA on the contributions.