It is fine to stop toprol one day and start atenolol the next day. they are the same class of medication. If you have no problems with Toprol, I suspect the same is true with the atenolol.
Good luck, I hope it works for you.
I take atenolol 100mg daily in divided doses , basically 25mg 4 times daily works much better that way, I rarely have PVCs anymore. I would imagine though I'm not a doctor, that the next day after you take the last dose of toprol you can take the atenolol, I was switched from propranolol to atenolol within a day. Double check with your doc first , though the Doc here on the forum will probably give you the best advice as what to do, good luck.