Your main delay here is the client polling interval.
You essentially have three choices, either reduce the polling interval globally in SCCM for all clients, change the policy polling interval for a specific collection or force the individual machine to poll now. (you can of course set an advert up well in advance with a scheduled time on it to get it installing at a specific time, but that doesn't sound like what you're asking)
Change the policy for your SCCM site from the Config Manager console, go into Site Database -> Site Management -> SITENAME -> Site Settings -> Client Agents, then open up properties on the Computer Client Agent and on the first tab you should see the Policy Polling Interval change the number of minutes here to set how often the machines poll back to SCCM for updated policies (default is every 60 minutes, setting it to anything less than 15 minutes is not advised).
If you want to get a group of PCs to poll more often than the rest, you can set a collection specific policy polling interval by right-clicking a Collection, selecting Modify Collection Settings clicking the Advanced tab, and then ticking the Enable collection specific policy polling interval box (again setting this to less than 15 minutes is not advised). Note that this collection setting won't be picked up by clients until their next polling time according to their previous schedule, so won't help you if you suddenly need to push something out immediately and unexpectedly, and haven't put the machines in this collection in advance.
Finally you can force an individual client to poll now, either by physically going to the PC and Initiating the Machine/User Policy Retrieval & Evaluation Cycle from the Configuration Manager control panel applet.
Alternatively there are tools you can use from a remote machine to do similar stuff on a machine by machine basis (assuming that your account has enough permissions). For instance SCCM Client Center is one thing that you can load on your PC and use to connect to remote SCCM clients, once you're connected you can use the Client Actions menu to initiate Download/Apply Machine/User Policies. There are also other similar tools out there including ones that integrate into the SCCM Admin Console as a right-click action on machines.